10 
EMBRYONIC DEVELOPMENT 
II. 
THE FECUNDATION. 
The phenomenon of the fecundation is one of the most difficult to investigate experi- 
mentally, and one of the most difficult also for the mind to understand in its effects. 
There is one feature in the egg’s history which is well established by observations : 
an egg does not develope into a new being unless it has been previously fecundated. 
In the fecundation there is a material action, which we may perchance witness the 
taking place of, and an immaterial act beyond the reach of our experiments. 
Thus, it is necessary that the seminal fluid should come into contact with the eggs 
in order to effect the required act. The spermatic particles may then be observed 
in great activity moving all around the egg, now and then darting at it from various 
points and striking it ; when at last, they become so much exhausted that they re- 
main immovable upon the egg until they vanish entirely away. Spermatic parti- 
cles I have not seen penetrating into the egg, therefore they do not, to my knowledge, 
constitute any part of the future being, but they act upon its surface, totally disap- 
pearing afterwards. Such is the material act of the fecundation. 
But, now, how are we to interpret that action? It causes a new being to be 
brought about, and which would not come forth without it : therein is the impalpable 
act of fecundation. 
Spermatozoa have been observed by several embryologists within the vitelline 
membrane, and even in the vitellus, but observation has not yet defined the part which 
they play in the phenomenon of fecundation. Is their presence, in the egg, necessary 
to the fulfilment of that mysterious act ? Do they constitute any integrant part of the 
future being? and if so, which part is it? Before any facts, answering the above 
queries, shall be experimentally demonstrated, no theory will ever have a chance of 
being adopted. The egg of Ascidia and that of Planaria are easily watched throughout 
their entire mass, and should a spermatozoon or spermatic particles penetrate into 
the vitellus, and constitute any part or portion of the future being, such a phe- 
nomenon could not escape the eye of a careful observer. If the union of the sper- 
matic substance with the vitelline substance is a necessary act in the procreation of the 
embryo, that union is molecular and beyond the reach of observation with the optical 
apparatus now at our command : when the spermatic particles lose their activity and 
disappear to the observer’s eye, they disintegrate into elementary molecules, in all 
probability minute cells, which enter the egg by endosmosis. That substance, in 
mixing with the vitelline substance, operates as a catalytic. For, no sooner has the 
phenomenon of the fecundation taken place, that the vitellus enters into the phases 
of the division, which is a mere kneading of the vitelline or embryonic substance. 
