170 



c). In Meriones Duval (5) has described large quantities of 

 megalokaryocytes of trophoblastic origin ; and has shown that this 

 rodeut possesses a capsularis. 



According to Fleischmann (12) the arrangement of the foetal 

 membranes in the Squirrel is similar to that in the Rabbit, while 

 Cricetus and Arvicola resemble the Mouse and Guinea-Pig in 

 possessing a capsularis. 



Chiroptera. 



a.) Microchiroptera. 



The first contribution to our knowledge of the placentation of 

 the Chiroptera was made by van Beneden (2, 3). Fuller accounts 

 have since been published by Frommel (13) and Nolf (33). Duval's 

 work has unfortunately remained unfinished. 



In the Europaean bats the placenta has the form of a concave 

 disc and is situated on the anti-mesometric side of the uterus. 

 Only one embryo is produced at a time, and it is always situated 

 in the right cornu. Ovulation may take place in either ovary. It 

 is an interesting fact that although copulation occurs in autumn, 

 fertilization does not take place till the following spring. 



The yolk-sac is larger at first than the allantois, but as the 

 latter, which has a large endodermal cavity, is developed it pushes 

 away the yolk-sac from its original attachment to the non- 

 embryonic hemisphere of the trophoblast. The area vasculosa how- 

 ever persists up till quite a late stage. 



The uterine glands open exclusively on the mesometric side. 

 Van Beneden showed that the uterine epithelium degenerated, even 

 before the trophoblast came into contact with it. According to 

 his first account the villi of the trophoblast then penetrated the 

 'couche dermatique raodifiée de la muqueuse uterine' ; subsequently 

 however, in a letter to Duval, he stated that the tissue covering 

 the 'cytoblastic' villi was a 'plasmodiblast', and, equally with the 

 former, of embryonic origin. 



Frommel's account is much more complete. He believed that 

 the uterine epithelium disappeared, and that the ectodermal (tro- 



