THE BAY OF BISCAY. 247 



Under the influence of fecundation, all the parts 

 of the egg of the Hermella and of the Teredo are 

 changed into an animal. The entire mass of these 

 parts is transformed into tissue, the external mem- 

 brane becoming the skin of the new being. Here 

 we have in truth a metamorphosis in the strictest 

 sense of the word. As phenomena more or less 

 similar to those which we have sketched occur in all 

 species, whether oviparous or viviparous, it follows, 

 that this expression, which has been proscribed by 

 evolutionists, ought rather to be generalised and 

 applied to the development of all living beings. 

 Embryology might, properly speaking, be defined 

 as the science of metamorphoses. 



The word metamorphosis would here assume a 

 general sense, and would designate the succession of 

 epigenetic facts, which produce from the germ either 

 a perfect plant or animal. Hitherto, however, it has 

 only been applied to those very apparent modifica- 

 tions which are experienced by certain animals after 

 their escape from the egg, and we will therefore 

 employ the term in its ordinary signification. Even 

 in this restricted sense, the phenomenon of metamor- 

 phosis is much more common than is generally sup- 

 posed. It was long regarded as a characteristic of 

 the class of Insects and of the group of the Batra- 



organised so as to give birth to larvae. Since I published these 

 researches, the results which I obtained have been confirmed by 

 different observers. I had even an opportunity of thoroughly demon- 

 strating this fact to some of my colleagues, in the case of the eggs 

 of the Unio, in which these phenomena are very well marked, al- 

 though perhaps they are not so striking as in the eggs of the Hermella. 

 u 4 



