OF PLANOCERA ELLIPTICA. 309 



tents already showed the egg : a vitellus or yolk, composed of small nucleated and 

 homogeneous cells. These vitelline cells filling the whole of the yolk's sphere with- 

 out any tendency of being more particularly crowded around the germinative vesicle 

 (fig. 1 — 4). The vitellus itself was semi-transparent, owing to the small amount of its 

 substance, then in process of formation. 



The germinative vesicle is proportionally large and the germinative spot small, 

 compared to the egg itself. The microscopic powers, then at my command, 

 could not reach the structure of their contents. 



A few weeks before they are laid, the eggs appeared as represented in figs. 5 and 

 6 : nearly full grown. The mass of the yolk has increased so as to render the sphere 

 entirely opaque (fig. 5). A transparent area, however, is seen upon one point where 

 the germinative vesicle approximates to the surface of the sphere (fig. 6). At this 

 stage of development, the germinative spot could no longer be perceived. The out- 

 line of the germinative vesicle itself became vague as if on the eve of disappearing 

 also. It, however, does not disappear entirely before the eggs are deposited. 



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 fiuid 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 action 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 



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