536 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The sj^ermatozoa, wliicla are derived from these last, obtain their 

 nutriment from the nucleus or the protoplasm of the male cell. 

 When completely develoj)ed they are detached, become free, and are 

 capable of acting as male elements. The nucleus undergoes dis- 

 aggregation. 



Between the early history of spermatogenesis and oogenesis there 

 is a remarkable resemblance, but there is a difference on which the 

 author specially insists ; in the female element the multiplication of 

 the ovular elements is generally limited to an early period, so that 

 the female tubes of Pfliiger contain a proportionately small number 

 of ovules, each of which is of a considerable size, while, on the other 

 hand, the male cells undergo a relatively more numerous series of 

 segmentations, and the resulting elements are large in number and 

 small in size. The view of many authors that the fundamental 

 process of spermatogenesis is a simple succession of cell-divisions, 

 ending in the formation of a cell small enough to be a spermatozoon is 

 erroneous. 



The essential conditions of oogenesis are the following : — 



A cellular element of the tissue of the ovary (not specially an 

 epithelial cell) grows and acquires a more important layer of proto- 

 plasm ; the nucleus multiplies more or less by division ; each of the 

 nuclei acquires an atmosphere of protoplasm, and we thus have the 

 female tubes of Pfliiger. The fundamental distinction only becomes 

 apparent in the fourth stage, when the ovules, increasing in size, 

 become differentiated by segregation and concentration, that is, by 

 the formation of corpuscles, more or less hyaline, which make their 

 way to the surface of the ovule. Here the essential difference com- 

 mences, for in one case the centrifugal elements are developed and 

 organized at the expense of the central element or nucleus, which is 

 lost in the nourishment of the peripheral elements, in the other 

 cases it is the centrifugal or peripheral element which is broken up 

 or serves as food for the development of the central element, which 

 then forms the egg. 



From these facts it is clear that the two elements of different 

 sexualities are the result of the elimination of one of them from a 

 cellular body which at first possessed them both, and were, therefore, 

 capable of a parthenogenetic mode of development. 



^ The theory of sexuality put forward by Sabatier allows us, in his 

 opinion, to understand how it is that one and the same sexual gland 

 may, as in the ovotestis of hermaphrodite molluscs, give rise to both 

 male and female elements, as well as such cases as those of Bufo, 

 where one end of the organ is male and the other female ; the theory 

 applies likewise to the occasional hermaphroditism in Vertebrates, 

 which, most pronounced in Serranus, has been noticed by various 

 observers in other Vertebrates, and even in man (Heppner). 



The sexual element is not always completely differentiated after a 

 single elimination ; two or even more may be necessary, and this is 

 especially the case with the female. The sexuality of the reproductive 

 cell is due to the appearance of the precocious globules or " globules 

 de debut " ; though a cell which has suffered such an elimination is 



