RELATIONS OF OVA AND GEMMAE. 195 



from the same mass of parenchyma. The latter observer 

 distinctly states that no difference can be detected in their 

 initial development. If the common eggs are, from their 

 producing young without impregnation, to be considered as 

 really gemmae, and of a different nature from the ephippial, 

 there is nothing at first to indicate this in their structure, 

 any more than in their substance or place of origin, for they 

 contain an equally distinct germinal vesicle, and are formed 

 side by side with the others, so that it is impossible to 

 determine at first which line of development any particular 

 germ will follow.* 



In the Rotifera, there is a similar distinction of com- 

 mon and winter eggs, though here there is some reason to 

 believe that it is the latter which are developed without fe- 

 cundation. In this group, according to Huxley, the true 

 ova are single cells, which have undergone a special develop- 

 ment ; the winter eggs are aggregations of cells, larger 

 or smaller portions sometimes, in fact, the whole 

 of the ova,ry, which become enveloped in a shell, and 

 simulate true ova.-)- 



4. For cases affording, if possible, still more cogent 

 arguments for the essential identity of gemmae and ova, we 

 may turn again to the class of Insects, where some late 

 researches go to show that bodies, not only having all the 

 structural characters of true ova, as in the cases quoted, 

 but under certain circumstances acquiring, as it would 

 seem, a capacity for impregnation, or, indeed, actually be- 

 coming impregnated, and thereupon undergoing the usual 

 embryonic development, may at other times be evolved into 

 normal organisms, without ever coming in contact with the 

 spermatic particles. Phenomena of this kind have been 

 rigorously demonstrated by Siebold, who proposes to restrict 



* Lubbock in Philos. Transact, for Jan., 1857, and Dec., 1858 ; Baird's 

 British Entomostraca (Ray Soc.), pp. 79, 87, 149. 



f Quarterly Journal of Microscopic Science, vol. L, pt. 1, p. 16. 



K 2 



