250 METAMOEPHOSES OP MAN 



step by step the development of the germs in both 

 viviparous and oviparous individuals. He thus demon- 

 strated prominently the distinctions, as to origin, 

 between the true and false ovum. The distinctions, 

 in some measure involuntarily, drawn by the distin- 

 guished Professor in the u School of Mines " are very 

 striking, especially to those who have observed the 

 embryogeny of some of those animals which, like the 

 Annelida and most marine Mollusca and Eadiata, are 

 best adapted to this class of investigations. 



In the viviparous individuals there occur pheno- 

 mena resembling those which I have met with not 

 only in Hermella and Teredo, but in hundreds of other 

 animals belonging to the three sub-kingdoms. In 

 the three last chambers of the ovary of the oviparous 

 Aphis figured by Huxley, the ovum in its embryonic 

 state is represented by an isolated but well-marked 

 germinal vesicle, which already exhibits its germinal 

 spot. This vesicle increases in size as it passes 

 through the second chamber^ but it is in the third 

 alone that it begins to be surrounded by the vitellus, 

 whilst the germinal spot remains still clear and 

 distinguishable. 



The only difference that I can observe between 

 the ova of these insects and those of the marine 

 animals to which I have referred is, that we see the 



my studies of marine animals. In such instances the phenomena 

 accompanying the earlier stages of development are presented even 

 to the uninquiring eye. The very opportunity which I have had of 

 forming a definite conclusion since the appearance of Professor 

 Huxley's memoir, is to my mind the most convincing proof of the 

 value of this work. In publishing it, the author has once more 

 shown that he deserves to be regarded as one of the most distin- 

 guished representatives of physiological zoology. 



