PLACENTAL STRUCTURES OF THE TENREC. 309 
Professor Kdlliker (J. c. p. 169), whilst adopting Weber’s class of deciduate Mammalia, 
has divided his non-deciduate class into two, the first of which is represented by the 
Pachyderms, and the second by the Ruminants. Of the first of these he says, ‘‘ The 
placenta is wholly wanting, the connexion of the ovum with the uterus is quite loose, 
the chorion carries well nigh over its entire surface small villuli (Zéttchen), which insert 
themselves into slight (leichte ? seichte) depressions of the uterine mucous membrane 
(type of the Pachyderms, or of the Pig).” Of the second we read, ‘‘ There is an inti- 
mate union of maternal and foetal structures; yet maternal and fcetal placente are 
separable without any tearing of tissues.” It is true that the cotyledon and the caruncle 
of the Ruminant are visible to the naked eye, and the villus and shallow pit of the 
Pachyderm are best seen with the help of a lens; but this seems scarcely a sufficient 
ground for such a bifurcation as that made by Professor Kolliker. And when we con- 
sider, further, that an undoubted Ruminant, the Camel, possesses a diffuse placenta and 
no cotyledons, and that, according to Professor Owen’s suggestion’, the pigmy Musk- 
Deer (Tragulus) will probably be found to be similarly organized, whilst the undoubtedly 
Suine Peccary (Dicotyles torquatus) approximates markedly to the Ruminants? not only 
by the increase of the stomachal cavities, but also by the decrease of the number of its 
offspring, this secondary division of the non-deciduate Mammalia will appear to be even 
less justifiable morphologically. 
Leaving now the consideration of the points in which the non-deciduate Mammalia 
resemble or differ from each other, I will pass in review certain statements which have 
been made as to the relation of their placental structures to those of the Rodents. In 
the excellent ‘ Vergleichende Anatomie und Physiologie’ of Bergmann and Leuckart I 
find, at p. 632, the following comparison :—‘‘ To these cotyledons (of the Ruminant) the 
single disk-shaped placenta of the Rodents has a strong resemblance, inasmuch as in their 
case also the maternal part usually projects notably out from the surface of the uterus 
in the shape of a button.” (‘‘ Mit diesen Cotyledonen hat die eine scheibenformige 
Placenta der Nager viel Aehnlichkeit, indem auch hier der miitterliche Antheil bedeutend 
knopfférmig aus der Flache der Uterus hervorzuragen pflegt.’”’) This comparison may 
seem to be amply borne out by a reference to my figure 5, which might serve, though 
but roughly, for a representation of a vertical section of a single cotyledon of a Ewe. 
But though the appearance of the parts may be much alike, their history and physiology 
is very unlike. The structure lettered ps” gives way in the Rodent and allows the cup- 
like mass which it attaches to the uterine wall to drop freely into the uterine cavity ; 
if it gives way in the Ruminant, as it sometimes does, it is a pathological process which 
entails, pro tanto, sterility upon the animal in which it occurs, and has its occurrence 
marked by the production of a cicatrix. In other words, the fibro-plastic cells which 
may be found on the utero-placental area of a Ruminant, from which the structure p s of 
figure 5 is accidentally separated, are not sufficient for the regeneration of the mucous 
* Hunter’s ‘Essays and Observations,’ p. 135. note 3. 2 Ibid. p. 124. note 3, and p, 125. 
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