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.* “TJ 
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. Kuprrer, as already mentioned, has even doubted that the micropyle 
plays any essential part in fertilisation (No. 87, p. 179); and Borck 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 suftice 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 Clwpea 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 Towopneustes variegatus) that while one usually enters, several may 
find access, and normal development still follow. Three or four indeed sometimes enter, 
as Herrwie and Fou 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 CauBeria’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). Kuprrer and Beyeck®, again, found that several sperms 
* Doyére had previously seen the micropyle in Syngnathus, 
