104 



ON CLASSIFICATION. 



The Cheiroptera, Insectivora, and Kodentia agree with Man 

 in possessing a placenta which is not only as much " discoidal," 

 allowance being made for the shorter curve of the uterine walls, 

 as his, but also entirely resembles his in being developed in 

 conjunction with a decidua. This decidua always corresponds 

 to at least the decidua serotina of Man ; frequently there is a 

 well-developed decidua reflexa* How far a decidua vera can 

 be said to be developed is doubtful. 



I am well aware that these statements are in direct opposi- 

 tion to some that have been very confidently put forward. 

 Thus, Professor Owen, in arguing against the views enter- 

 tained by Milne-Edwards and Gervais, makes the following 

 assertions : — 



" The degree of resemblance in outward form between the 

 placenta of the Eat or Hare, on the one hand, and the Mycetes 

 and Macacus on the other, seems to me to be more than 

 counterbalanced by the difference of structure. The pedunculate 

 and cotyloid placenta of the Bat consists of foetal parts exclu- 



Fiff. 42. 



Fig. 42. — Magnified view of a section of the placenta and uterus of a pregnant Rat. 



sively ; the maternal areolar portion is as distinct from it as it is 

 in the cotyledon of the Ruminant, and is a persistent structure of 



* See upon this subject the recently-published valuable essay of Eeichert : 

 "Beitrage zur Entwickelungs-geschichte des Meerschweinchens." Reichert finds 

 a complete, or almost complete, decidua reflexa in Rats, Mice, Guinea-pigs, and 

 Bats; while in Rabbits, Hares, and Camivora, the decidua reflexa only partially 

 surrounds the ovum. 



