106 ON THE PLACENTAL STRUCTURES OF THE TENREC 



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 whole surface small villuli (Zott- 

 chen) 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, 

 1 There is an intimate 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 the 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 consider, further, that an 

 undoubted ruminant, the camel, possesses a diffuse placenta and no 

 cotyledons, and that, according to Professor Owen's suggestion l , 

 the pigmy musk deer (Tragulus) will probably be found to be 

 similarly organised, whilst the undoubtedly swine peccary (Dicotyles 

 torquatus) approximates markedly to the ruminant 2 not only by the 

 increase of the stomachal cavities, but also by the decrease of the 

 number of its offspring, the 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 c Vergleichende Anatomie und Physiologie ' of Berg- 

 mann and Leuckart I find, at p. 6^1, 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 out from the surface of the uterus in the shape of a button (' mit 

 diesen Cotyledonen hat die eine scheibenformige Placenta der Nager viel Aehnlich- 

 keit, indem auch hier der Mutterliche Antheil bedeutend knopfformig aus der 

 Flache der Uterus hervorzuragen pflegt '). 



This comparison may seem to be amply borne out by a reference 

 to 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 downgrowth of deciduous serotina 



1 Hunter's 'Essays and Observations,' vol. ii. p. 135. note 3. [The diffused form of 

 placenta has been described by M. Alphonse Milne Edwards in Tragulus, and by 

 the Editor and the late Prof. Garrod in Hyomoschus aquaticus. ' Proc. Zool. Soc.' 

 June, 1878.] 2 Ibid. p. 124. note 3, and p. 125. 



