RECENT RESEARCHES ON SPERMATOGENESIS. 321 



count are by M. Duval, who has chosen for the investigation of 

 the general phenomena of Spermatogenesis the snail, with other 

 Pulmonate Gastropods, and the frog. Both of these animals 

 were also chosen by myself, though I took my earliest type 

 from the lower divisions of the animal kingdom, in the sliape 

 of the earth-worm, an animal which exhibits the phenomenon 

 of Spermatogenesis, as found in the majority of the Vermes, 

 with singular clearness and facility for study. 



M. Duval's first communication on the subject is published 

 in the 'Rev. de Science Nat./ tome vii, June, 1878, in which 

 he treats of Spermatogenesis in Pulmonate Gastropods, and 

 takes Helix as the typical representative of the class. Had I 

 been aware of the existence of this paper when I published 

 my researches over the same ground I should have referred to 

 it then, but I did not discover its existence till too late. 



M. Duval commences by showing the importance of ex- 

 tending observations which apply to animals whose time of 

 procreation is limited to a definite period of the year, over 

 sufficient time to embrace the whole process, not as many have 

 done, making observations only at one time of the year, and 

 then drawing conclusions from observations which are, of 

 course, imperfect. Taking the condition of the ovotestis as 

 it exists in the winter, it is found to contain a few bundles of 

 spermatozoa and some free spermatozoa, while its wall is lined 

 with indifferent cells, to which he gives no particular name, 

 but which obviously correspond to the testicular and ovarian 

 epithelia. In the spring certain of these cells are seen to 

 enlarge, some rapidly, so that it soon becomes obvious that 

 they are destined to form the ova, while others grow more 

 slowly, and never attain the same size. These he calls male 

 ovules, and they form the starting-point from which the sper- 

 matozoa are evolved. These male ovules consist of granular 

 cells containing one well-marked nucleus. The first change 

 they undergo consists in the development of other nuclei by 

 endogenous formation, which, by their further multiplication 

 by division, form the immature spermatozoa or spermatoblasts. 

 And here is the first point where his observations differ from 



