482 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



help giving in our adhesion to so much of the 

 doctrines of Sabatier as are contained in his thesis 

 that all cells are originally hermaphrodite, and that 

 some by losing one element, and some the other, 

 become distinctively male or female cells. Balfour 

 has enunciated the striking and bold hypothesis that 

 the function of forming polar cells was acquired by 

 the ovum with the object of preventing partheno- 

 genesis ; the strongest support for this doctrine was 

 found by Balfour in the reported absence of polar 

 globules in the only two divisions of the animal 

 kingdom (Rotifera and Arthropoda) in which we 

 normally find development of ova without male 

 influence. On the other hand, Billet, with a full 

 knowledge of the facts, and of Balfour's hypothesis, 

 has lately recorded the presence of polar globules in 

 the Rotifera, and Grobben has given a less pointed 

 account of the formation of the same bodies in some 

 of the lower Crustacea.* The remaining portion of 

 the original nucleus returns to the centre of the egg, 

 where it forms the female pronuclews. The 

 mature egg, or female element, requires the addition 

 of the male element or spermatozoon, before it can 

 set out on the course of its development. When 

 brought into the neighbourhood of the male cell we 

 find that an egg will receive one or more spermatozoa, 

 but that, if fresh and uninjured, not more than two or 

 three pass into it ; if they do the future of the egg is 

 endangered. As a rule, only one spermatozoon enters 

 into and becomes a constituent of the protoplasm of 

 the ovum ; the tail of the male cell disappears, but its 

 head persists for a time as a distinct structure ; this 



* The student will not fail to observe that, at the present time, 

 a well-conducted and carefully described series of observations on 

 a selected form may affect very deeply the speculations of previous 

 students. Conversely, philosophical speculations have a gxiiding 

 influence on lines of study. 



