108 



ON CLASSIFICATION. 



placenta in all genera which have been examined (except the 

 Polecat, according to Von Baer) has the form of a complete zone, 



Fig. 4:i 



Fig. 43. — Foetal kitten, with its membranes and placenta. The latter is seen from within, 

 the chorion and allantois being open and everted. — Am, amnion ; All, allantois ; PI, 

 placenta ; Um, umbilical vesicle. 



(From a preparation in the Museum of the Royal College of Surgeons.) 



or broad girdle, surrounding the middle of the chorion and 

 leaving the poles bare (Fig. 43). 



Thus Man ; the Apes, or so called Quadrumana ; the 

 hisectivora ; the Cheiroptera ; the Pioclentia, to which the lowest 

 apes present so many remarkable approximations ; and the 

 Carnivora (united into one group with the hisectivora by 

 Cuvier) are all as closely connected by their placental structure 

 as they are by their general affinities. 



With the Pig, on the other hand, all the Artiodactyla, all the 

 P erissodactyla (save one, taking the group in its ordinarily 

 received sense) and all the Cetaeea which have been studied, 

 agree in developing no decidua, or, in other words, in the fact 

 that no vascular maternal parts are thrown off during parturi- 

 tion. But considerable differences are observed in the details 



