THE OVUM OF THE NINE-BANDED ARMADILLO. 127 



marsupial Dasyurus. In the sense that the ovum is like that of a 

 member of a lower sub-class of mammals it may be considered as 

 probably the most primitive Eutherian ovum on record. The 

 deutoplasmic material is at first centrally situated within a 

 capsule of formative protoplasm, but, coincident with the onset 

 of maturation, a shifting of materials takes place, so that the 

 deutoplasmic material is aggregated at the animal pole of the 

 ovocyte while the formative protoplasm forms a cap-shaped mass 

 at the vegetative pole. The first polar spindle occupies a position 

 as near the animal pole as it can without leaving the surface of 

 the cell or the formative material. The earlier condition may 

 be called " centrolecithal " and the later, "telolecithal," though 

 these terms probably imply homologies that do not exist. 



2. Previous studies of mammalian ovogenesis are confined to 

 three orders of mammals, Rodentia, Cheiroptera and Carnivora, 

 all of which are rather highly specialized orders, according to 

 modern systems of classification. The present study of condi- 

 tions in the armadillo is the first contribution to our knowledge 

 of the germ cells of the Edentata, and thus we may add not only 

 a new order to the short list of those studied, but probably the 

 order showing the most primitive conditions. 



3. Since it had not been found feasible to breed the armadillos 

 in captivity our knowledge of the maturation processes depends 

 entirely upon studies of the ovarian ova, normal and atretic. 

 Nine tenths of the process as here described takes place in normal 

 follicles and hence must be considered as strictly normal. A 

 large number of ovaries have been sectioned in order to secure 

 the stages described in the present history. Abundance of 

 material is necessary because some of the stages are of exceed- 

 ingly rare occurrence. 



4. A study of the developmental history of the follicle shows 

 that there is no basis for the idea expressed by Rosner that the 

 four embryos are derived from the fusion of four adjacent follicles 

 and the cooperation of their four ova to form a compound 

 blastodermic vesicle. 



5. The full grown ovum is about .12 mm. in diameter. It is 

 smaller than that of the cat and larger than that of man. 



6. The first polar spindle and first polar body are in no way 

 radically different from those described for other mammals. The 



