86 



MORPHOLOGY. 



probably the iminediate result of impregnation ; for I have seen active spermatozoa a little before 

 this time in the cavity of the female gonophore. 



Until, however, we have farther evidence of what really becomes of the germinal vesicle. 



Fin. :V.). 



Develoiiment of the ovum in Laomedeaflexuosa. 



A, Youn^ ovum iu the gonophore previously to the disappearance of the germinal vesicle; the gerniiual vesicle is here 

 seen to contain several germinal spots. B, The germinal vesicle and spots have disappeared. C, The vitellus has hecome 

 cleft into two segmentation-spheres. D, The ovum after the second cleavage. E, The segmentation-spheres have become 

 numerous, and many of them now show a distinct nucleus. F, The segmentation-spheres have greatly increased in 

 numbei-, and a nucleus may now be detected in each of them. G, The segmentation-spheres have still further increased 

 in number, while the most superficial have become arranged into a stratum distinguishable from the deeper portion of 

 the ovum. H, The superficial stratum has become more distinct, and is now seen to he composed of long prismatic cells. 

 I, The ovum has begun to elongate itself, and one end has become folded on the remainder. K, The embryo just after 

 its escape in the form of a ciliated planula. 



it is nseless to speculate upon the influence which the supposed liberation of its contents 

 may exert in exciting the new series of phenomena which arc now about to take place in 

 the ovum ; at all events, shortly after the disappearance of the germinal vesicle, the process of 

 segmentation sets in. This process is certainly not preceded by the visible occurrence of a new 



