692 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



The artificial fertilisation of the eggs of osseous fishes is easily performed, it being 

 only necessary to apply ripe spermatozoa (PI. I. fig. 9) from the male to mature ova 

 placed in water. If ova and the male element be placed in the same vessel of water, the 

 process is accomplished in a few moments. The exact mode by which it was really 

 accomplished remained unknown until Ransom not only saw and truly interpreted the 

 micropylar opening, but watched spermatozoa make their way into the aperture. # " I 

 saw," he says (No. 127, p. 461), "an active spermatozooid enter the apex of the funnel, 

 and disappear as if inwards ; a quarter of a minute more had not elapsed before the bright 

 circle which marks the aperture became indistinct from shortening of the funnel ; during 

 the next two minutes I saw three more spermatozooids enter the apex and vanish 

 apparently inwards." Notwithstanding the clear and unmistakable observations pub- 

 lished by Ransom, the process of fertilisation is one about which much discussion has 

 taken place. Kupffer, as already mentioned, has even doubted that the micropyle 

 plays any essential part in fertilisation (No. 87, p. 179) ; and Boeck has advanced a 

 theory of endosmosis which is somewhat like the explanation Newport put forward in one 

 of his earlier treatises, when, having failed to detect in the ovum of Rana any perforation 

 or fissure by which sperms could find access to the egg-contents, he said that mere contact 

 with the external envelope must suffice for fertilisation, as he never found spermatozoa in 

 contact with the yelk-membrane, or even within the substance of the external envelope 

 (No. 112, p. 203). This endosmotic theory Newport afterwards abandoned, and adopted 

 the opinion which Dr Martin Barry had put forward — in accordance with the views of 

 Leeuwenhoek, and Prevost and Dumas (No. 121), that the spermatozoa penetrate bodily 

 into the ovum (No. 21, p. 309). Ransom's explicit account decides the matter, the situa- 

 tion and structure of the micropyle clearly indicating its purpose, viz., the admission of 

 the spermatozoa to the germinal elements within the ovum (No. 127, p. 462). G. Brook, 

 again, has recently affirmed that in Clupea spermatozoa enter on all sides. The interesting 

 question remains as to whether one or more spermatic bodies are concerned in the normal 

 fecundation of a single ovum. The presumption that one spermatozoon suffices is 

 strong, but there are peculiar difficulties in the case of the Teleostean ovum in actually 

 observing the fact. The entrance of these bodies has been watched in many Inverte- 

 brates, and one spermatozoon is usually found competent to effect fertilisation, though 

 Selenka found (in Toxopneustes variegatus) that while one usually enters, several may 

 find access, and normal development still follow. Three or four indeed sometimes enter, 

 as Hertwig and Fol observed in the same species, and the separate pronuclei formed by 

 each usually fuse with the single female pronucleus ; but they found that subsequent 

 cleavage was irregular (No. 66). In Petromyzon Calberla's investigations show that 

 one sperm only enters, the enlarged head-portion separating at the outer micropyle from 

 the tail which is left behind, while the head penetrates the yolk or rather passes along a 

 protoplasmic process, which penetrates the yolk and reaches the female pronucleus at the 

 inner extremity (No. 38, p. 464). Kupffer and Benecke, again, found that several sperms 



* Doy£re had previously seen the micropyle in Syngnathus. 



