The Development of the Amphibian Kidney. Part III. The Post

33 Pages·2006·6.24 MB·English

The Development of the Amphibian Kidney.
Part III. The Post-Metamorphic Develop-
ment of the Kidney, and the Development of
the Vasa Efferentia and Seminal Vesicles in
Rana Temporaria.
By
Peter Gray, Ph.D., D.I.C.,
Lecturer in Vertebrate Embryology, Department of Zoology, Edinburgh
University.
With Plates 20 to 23 and 3 Text-figures.
CONTENTS.
INTRODUCTION . . . . . . . .. 445
A. MATERIAL AND METHODS . . . . . .. 446
B. POST-METAMORPHIO DEVELOPMENT OF THE KIDNEY
i. Attachment of units to archinephric duct . . .. 446
ii. Production of accessory peritoneal funnels . . . 451
C. DEVELOPMENT OF THE VASA EFFERENTIA
i. Historical Summary . . . . . .. 454
ii. Origin . . . . . . . .. 458
iii. Subsequent Development . . . . .. 458
D. DEVELOPMENT OF THE SEMINAL VESICLES
i. Historical Note . . . . . . .. 464
ii. Description . . . . . . . .. 464
iii. Possible Homologies . . . . . .. 465
E. REVIEW 466
F. SUMMARY 469
G. BIBLIOGRAPHY . . . . . . . . . 4 71
EXPLANATION OF PLATES . . . . . . . 4 72
INTRODUCTION.
THIS research forms Part III of the writer's investigations into
the development of the amphibian kidney, the two previous
parts (Gray, 1930, 1932) having dealt with the development of
the kidney of Eana temporaria and Molge vulgaris
up to a stage slightly beyond metamorphosis. The post-meta-
morphic development of the kidney units themselves shows
little of interest, but the method of their attachment, especially
446 PETER GRAY
in the post-metamorphic posterior region, is quite different from
that of the earlier generations. Our knowledge of the develop-
ment of the genital connexion, moreover, is very confused.
It is not the writer's intention, either here or in the future,
to redescribe the development of the oviduct, since he is con-
vinced, from his own observations, that the accounts of Hall
(1904) and MacBride (1892) are substantially accurate. It is in
the formation of the vasa efferentia, and in the passage of the
sperm through the kidney, that the main gaps in our knowledge
occur. The development of the seminal vesicle appears never to
have been worked out.
A. MATERIAL AND METHODS.
The material of this research is substantially that used by
the writer in his previous work on the frog (Gray, 1930) and will
be found fully described in that paper. The post-metamorphic
material has been collected from time to time, mostly in Nor-
folk. The young frogs were fixed in Bouin and stored in 70 per
cent, alcohol before the urinogenital organs were dissected out.
These have therefore been fixed in the shape they had during
life, and fig. 5, PL 20, and fig. 30, PI. 23, for example, are revealing
to those who picture the kidney as the smoothly oval structure
which appears in dissections.
Sections attached to the slide by the ordinary albumen
methods were found not to retain the blood corpuscles, and there-
fore sections, such as that shown in fig. 1, PI. 20, likely to contain
much blood were dipped in 0-1 per cent, celloidin in ether after
de-waxing in xylol and passing through absolute alcohol. The
ether was allowed to evaporate until diffraction colours appeared,
when the slide was dropped into 50 per cent, alcohol.
The reconstructions shown in figs. 8 and 9, PI. 21, were pre-
pared by the special reconstruction technique worked out by
the writer for his work on Triton (Gray, 1932).
B. POST-METAMORPHIC DEVELOPMENT OF THE KIDNEY.
(i) Attachment of units to archinephric duct.
No previous worker appears to have studied the post-meta-
morphic development of the kidney, and, in my previous woik
DEVELOPMENT OF AMPHIBIAN KIDNEY 447
(Gray, 1930), I was handicapped by a lack of material taken
between metamorphosis and sexual maturity in the fourth year.
The story which I then put forward is accurate so far as it goes, but
the three years following metamorphosis show great changes in
the posterior (non-sexual) portion of the kidney, more especially
with regard to the method of attachment of the units to the
archinephric duct.
The position in Rana is particularly complicated and differs
from Triton in that there is no clearly denned sexual region,
for the anterior portion of the male kidney has some excretory
function. The excretory and non-excretory regions grade into
each other. Each has its own special system for the connexion
of units to the archinephric duct. In the anterior, sexual region
the 'straight tubules' described in my previous research form
both the direct connexion between the vasa efferentia and the
archinephric duct and also serve for the attachment of such
excretory units as occur in this area. These straight tubules
also occur in the mid-region of the kidney, posteriorly to the
vasa efferentia, and there serve solely for the attachment of
excretory units. They are not, however, sufficient in number to
provide for the attachment of every unit, and large numbers of
secondary, arborizing, collecting-trunks arise from the blastema
which immediately surrounds the archinephric duct. During
the course of the second and third years after metamorphosis
the 'kidney' increases greatly in length, but this increase
is due solely to the addition of units to the
posterior region. No further transverse straight tubules
are formed, but these new units are taken up by numbers of
small collecting-trunks from the archinephric duct.
The fact that the kidney increases in length by additions to
its posterior region is well shown by an examination of the
relative position of the testis. Fig. 16, PI. 22, shows the appear-
ance of the urinogenital system of a 53-mm. Rana tern-
poraria, taken and fixed in Bouin in July: that is, one which
would have reached sexual maturity in about nine months'
time. Even at this late stage the testis appears to lie relatively
farther towards the posterior end of the kidney than in the adult.
The posterior region of the kidney, moreover, is clearly differ-
NO. 311 G g
448 PETER GEAY
entiated in the photograph both by its shape and by the greater
quantity of blood which it contains.
The posterior augmentation of the kidney, and the variation
in the types of attachment of the units must be clearly
grasped before any interpretation of sections can be given,
AT METAMORPHOSIS
3rd YEAR.
TEXT-FIG. 1.
Diagram to show the methods of attachments of units to the
archinephric duct between metamorphosis and sexual maturity.
AD., archinephric duct; AU., abortive unit; CT., collecting trunks;
BT., blind tubule; DC, developing collecting-trunk; DU., developing
unit; FU., functional unit; BBC, rudiment of Bidder's canal;
VE., vas efferens.
and the following explanation of Text-fig. 1 is therefore given
before the description of the sections upon which it is based.
A and B show the condition throughout the entire kidney at
metamorphosis. This is the condition which was described in
my last paper, but may be recapitulated here. As the archi-
nephric duct (AD.) has passed from the inner to the outer margin
of the kidney it has left, lying transversely across the dorsal
surface of the kidney, the straight tubule (ST.) ending in an
abortive malpighian unit (AU.). Functional units (FU.) have
become attached to this tubule in both regions. For a fuller
description of this process see Gray (1930, Text-figs. 6 and 7).
What is here referred to as the middle region (Text-fig. 1, B) is
DEVELOPMENT OF AMPHIBIAN KIDNEY 449
actually the hinder end of the kidney at metamorphosis, the
true posterior region (Text-fig. 1, E and H) being added during
the succeeding years.
In the sexual region (Text-fig. 1, C and F) the elaboration of
the sexual connexion is the only change; this is described more
fully in a later part of this paper. No further functional units
are added, and the straight tubule maintains its primitive
appearance.
In the mid-region, however (Text-fig. 1, D and G), there is
a considerable increase in the number of functional units (FU.)
which become connected to the straight tubule (ST.). This last
loses its primitive straightness and becomes pulled out from one
side to another as more and more tubules become attached.
At the same time its histological appearance becomes less
sharply differentiated from the excretory tubules which sur-
round it. Thus there arises a condition when no further room
can be found for such attachments, and a number of collecting-
trunks (DC.) arise. These are produced in situ from the
blastema which always surrounds the inner angle of the kidney.
Units (DU.) also arise in this area, in the manner already
described (loc. cit.), and become attached to the collecting-
trunks. The whole course of the development of these units and
of the collecting-trunks themselves is highly irregular. Thus in
the middle region of a third-year kidney (Text-fig. 1, G) there
are some units regularly attached to the straight tubules and
others which communicate with the archinephric duct through
an irregular system of branched, and even sometimes anasto-
mosing, collecting-trunks. The abortive unit which terminated
the original straight tubule finally degenerates, and it becomes
very difficult to decide, even by reconstructional methods, what
was a straight tubule and what is a secondarily developed
collecting-trunk.
In the posterior region, which becomes differentiated during
the beginning of the second year, there are no straight tubules.
There are, however, a considerable number of functional units
which are connected solely to the collecting-trunk network.
These are shown developing in Text-fig. 1, E, and are diagram-
matically represented at the conclusion of their development
450 PETER GRAY
in Text-fig. 1, H. As blindly ending tubules (BT., Text-fig. 1, E)
are occasionally found scattered among the developing units
and collecting-trunks in the posterior region, it is probable that
such anastomoses as there are have been produced by the
attachment of these blind tubules rather than by fusion be-
tween the trunks themselves. Moreover, it may be observed
that there is no spare blastema surrounding the archinephric
duct in the adult, and it seems probable that such blastema as
remains, after the formation of collecting-trunks and units has
ceased, may be used up in the formation of numerous little
accessory collecting-trunks. That such an anastomosing mass
exists is shown by the work of Stewart (1927), who records that
'under conditions of injection and dissection of the ramifications
of the collecting duct tree, it was not possible to make out in
many instances the junction of the collecting duct and its
distal convolutions. It is probable that there are many more
than seven orders in the collecting duct system'. His figures
show clearly that he was working upon a collecting-duct of the
mid or posterior region.
The existence of the straight tubule and its connexions is
very clearly seen in sections of the sexual region. Fig. 7, PI. 20,
represents a section across the extreme anterior end of the
kidney of a second-year frog. The straight tubule (st.) ends in
the abortive unit (au.). This most anterior of straight tubules
is without excretory connexions. Fig. 6 on the same plate is
from about 3 mm. farther back in the same series; the straight
tubule (si.) is still equally distinct but shows quite clearly
the attachments (ae.) of two functional units. At this period
there is no trace of collecting-trunks.
Collecting-trunks are best seen in sections of a third-year
kidney. Three sections from the same series of a 53-mm. frog
are shown on Plate 20. The most anterior of these, fig. 5, PI. 20,
is from the middle region. The straight tubule (st.) is not nearly
so sharply differentiated as it was in the two-year frog, but can
still be distinguished from the surrounding tissues.
The attachments (ae.) to the functional units are best seen
in the enlarged central portion of this figure reproduced as
fig. 17, PI. 22. By this time, however, collecting-trunks have
DEVELOPMENT OF AMPHIBIAN KIDNEY 451
appeared and show as small ducts (ct., fig. 5, PL 20) with deeply
staining nuclei. Fig. 1, PL 20, is taken towards the hinder end
of the kidney in the region where the archinephric duct (ad.) is
just passing away from the main mass. The last collecting-
trunk to be directly connected is shown leaving the archi-
nephric duct and is seen to be surrounded by minor collecting-
trunks (ct). Several developing glomeruli (dm.) are cut in this
section. The last section (fig. 2, PL 20) is taken through the
true posterior kidney, well behind the point of separation of
the archinephric duct. Even at this late age (three years) the
tissues still consist largely of blastema in which many developing
units appear. The collecting-trunks (ct.) which run backwards
from the more anterior point of attachment can again be clearly
differentiated by their histological structure.
The gradual loss of distinctness which is noticeable in the
straight tubule is well illustrated by fig. 3, PL 20. This is through
the middle region of a 42-mm. (second-year) frog. The straight
tubule, which here serves solely for the attachment of excretory
units, is beginning to coil in the manner indicated in Text-fig. 1,
so that it appears cut in several places. It is more readily
distinguishable from the surrounding excretory tissues than will
be the case a year later (fig. 5, PL 20), but is markedly less
obvious than it was a year before (figs. 6 and 7, PL 20).
To sum up, then, the methods of unit attachment shown in
the post-metamorphic kidney, there are, passing from anterior
to posterior:
(1) One, or at the most two, anterior straight tubules devoted
to the carrying of sperm.
(2) A further series of three or four straight tubules which
carry both sperm and excretory products.
(3) About six 'straight tubules', later becoming bent, which
carry only excretory products.
(4) A number of posterior collecting-trunks which are pro-
duced irregularly and anastomose among themselves.
(ii) Production of Accessory Peritoneal Funnels.
It was noted in Part I of this investigation (this Journal, vol.
73, pp. 533-7) that there are two methods for the production
452 PETER GRAY
of peritoneal funnels. The first, the only one figured by previous
writers, is by separation from a primary unit; the second is
through the action of special funnel-forming tubules which
follow the course of the surface veins along whose coelomic
walls the funnels develop.
During the second and third years after metamorphosis even
these special tubules appear insufficient to provide the very
large number of peritoneal funnels which are apparently neces-
sary to the animal. As noted (loc. cit.) the funnels are grouped
mostly in that region of the kidney which lies against the testis.
This region consists, even in the third year, largely of blastema.
This is well seen in fig. 5, PI. 20, where an accessory peritoneal
funnel (pf.) lies in the middle of this darkly stained blastema
mass.
These accessory funnels are formed in situ from the
blastema, first appearing as a cylindrical aggregation of cells
which soon becomes conical, with the base of the cone against
the peritoneal wall. A lumen then appears and the inner walls
of the hollow cone acquire cilia at about the same time as the
inner end makes contact with a renal venule. These accessory
peritoneal funnels are all much longer than those produced by
the first two methods described and occasionally acquire a bend
reminiscent of an excretory unit. There is no doubt that they
represent complete units which, from their position, are out
of the sphere of influence of a straight tubule and therefore
do not acquire excretory connexions, and it is not difficult to
imagine that this lack has led to the suppression of the mal-
pighian capsule.
One of the most remarkable features of these long funnels is
the close association of the long tail with the renal arterioles.
In fig. 10, PL 22, for example, one of these funnels (pf.) is seen
lying close to the venule into which it will ultimately open.
The renal arteriole, lying to the right of the venule, was noticed
to be of unusual size and, on being followed back to its source,
was found to be directly connected to the renal artery and to
throw out no branches before reaching the neighbourhood of
the peritoneal funnel. After lying for a short distance in close
association with the tail of the funnel, the arteriole loops back
DEVELOPMENT OF AMPHIBIAN KIDNEY 453
into the main mass of the kidney where it splits, in the ordinary
manner, into numerous branches to the glomeruli of secondary
malpighian capsules, and to the excretory portions of the
secondary tubules.
These accessory funnels increase their number by direct
splitting from the end of the tail to the funnel, as is seen in
fig. 15, PI. 22. It will be noticed also that the renal arterioles
(r.at.) are similarly doubled, one branch being associated with each
tail of the funnel. Only one of these tails is cut, and is seen lying
just above the larger artery; the other runs directly away from,
and in a plane at right angles to, the observer.
It is fairly universally accepted that the function of the
glomerulus is confined to the adjustment of the water content
of the blood and that the excretion of nitrogenous waste takes
place through the renal tubules. It seems, therefore, very
probable that the tails of these accessory funnels may have an
excretory function, the waste products being passed to the
arterioles. If this is not so, there is no apparent reason for the
existence either of the tail, or of the special arteriole: if this
postulate be accepted, then the production, function, and
correlation of the whole series of peritoneal funnels becomes
clearer.
In Text-fig. 2 are shown two stages in the production of
a peritoneal funnel by each of the methods described. In A and
B the funnel, closely associated with, but not opening into, the
malpighian unit, directly connects the coelomic cavity with a
venule. The artery supplies both the water-adjusting glomeru-
lus and the waste-excreting tubule. This method is found only
in young tadpoles and is a relic, of phylogenetic interest, of the
urodele type. In E, which begins a few weeks before, and
continues for a few months after, the tadpole leaves the
water, special tubules connect the dorsal blastema mass to the
peritoneum. In C and D, which begins during the first and
continues during the second and third years spent by the frog
on land, the blastema has shifted to the peritoneal surface and
the tubules have acquired a tail with an arterial supply.
These observed facts of structure can be exactly correlated
with the observed habits. As a tadpole the larva is not subject
454 PETER GRAY
to loss of water, and the return of peritoneal fluid to the veins is
of small importance. As soon as it leaves the water, the cir-
culation through the cutaneous vein must lead to a considerable
increase in direct water-loss from the blood which must be directly
replaced by the return of peritoneal fluid; large numbers of
funnels are therefore produced at this period in the quickest
possible manner. Such an arrangement, however, results in the
mixing with the blood of large quantities of waste products
PR A
TEXT-FIG. 2.
Diagram to show the various methods by which peritoneal funnels
are produced. The hatching represents undifferentiated blastema.
A and B: from early units. C and D: accessory funnels from
surface blastema. E: from funnel-forming tubules, A., artery;
MC, malpighian capsule; FT., funnel-forming tubule; PF., peri-
toneal funnel; PW., peritoneal wall; v., vein.
picked up with the peritoneal fluid. Later funnels, therefore,
are furnished with a short length of tubule with the aid of which
the arteries can filter out the impurities from the peritoneal
fluid and pass this to the excretory tubules proper. If the
arteries had no special function to fulfil in this region they would
scarcely be expected to run directly to the region of the funnels
before passing to the kidney tubules.
C. DEVELOPMENT OF THE VASA EFFERENTIA.
(i) Historical Summary.
The formation of the vasa efferentia and the course of the
sperm through the kidney have been the subject of so much