PLACENTAL STRUCTURES OF THE TENREC. 309 



Professor KoUiker (Z. c. p. 169), whilst adopting Weber's class of deciduate Mamraaliti, 

 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 (Zottchen), 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 foetal placentae 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 KoUiker. 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 Anatomic und Physiologic ' 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 

 knopfformig 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 d s" 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 d 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. ' Ibid. p. 124. note 3, and p. 125. 



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