April 1892.] THE BOTANICAL SOCIETY OF EDINBURGH. 415 



(cyto) plasm, and which is the real carrier of the hereditary - 

 substance. 



After this short account of the more recent theories as to 

 the origin of sex, we must proceed to a study of the signifi- 

 cance of the various phenomena observed during the act of 

 fertilisation, and see how these phenomena have been inter- 

 preted by the various investigators. 



Martin Barry (1843) seems to have been the first who 

 observed spermatozoids in the ovum of the rabbit. Leuckart 

 made the same observation in the frog (1849), Nelson in 

 Ascaris mystcx (1852), and Keber observed the actual en- 

 trance of the spermatozoon into the egg of the common 

 mussel. How the spermatozoon affected the egg was not 

 known till, in 1872, Blitschli observed two nuclei in the 

 fecundated egg of Rhcibditis doliclmra, and till, in 1874, 

 Auerbach, quite independently, made the same observation 

 in two other worms, Ascaris migrovenose and Strongylus 

 auricularis. To 0. Hertwig (1875), however, belongs the 

 credit of having; demonstrated that the second nucleus is 

 the head of the spermatozoon. Hertwig, however, at first 

 supposed that the other nucleus was the germinal spot 

 of Wagner, set free by the destruction of the germinal 

 vesicle, an error which was corrected by Van Beneden, 

 and the other nucleus was soon shown to be, as Blitschli 

 had previously conjectured, the germinal vesicle. Van 

 Beneden further described (1875) the fusion of the two 

 nuclei, and compared this fusion to the conjugation of the 

 Protonozoa and Protophyta, and in 1883 advanced our know- 

 ledge on this subject greatly by his magnificent monograph 

 on the fecundation of Ascaris nicgalocciJliala. Pol (1877), 

 however, not only observed the entrance of the spermatozoid 

 into the eggs of Asterias glacialis, Echinus, &c., but also 

 figured the phenomena that ensued, phenomena confirmed 

 by many naturalists.* I cannot do better than describe 

 these phenomena in Hertwig's words : — " The egg sends 

 out a projection to meet the spermatozoon, and then takes 

 it up into the interior of the yolk. 



" In the protoplasm of the egg the achromatic end of the 



* For this short historical account I am indebted to Prof. M'Kendriek, who, 

 in his text-book of Physiology, pp. 223, 224, has given above account, which, 

 apart from the condensation, has been copied almost literally. 



