246 ALTERNATE GENERATIONS. 



These transformations do not correspond to our 

 common idea of metamorphoses, as observed in 

 the Insect, for instance. In the Butterfly's life 

 we have always one and the same individual, — 

 the Caterpillar passing into the Chrysalis state, 

 and the Chrysalis passing into the condition of 

 the Winged Insect. But in the case I have been 

 describing, while the Hydroid gives birth to the 

 Medusa, it still preserves its own distinct exist- 

 ence ; and the different forms developed on one 

 stock seem to be two parallel lives, and not the 

 various phases of one and the same life. This 

 group of Hydroids retains the name of Coryne ;* 

 and the Medusa born from it, the Sarsia (repre- 

 sented on p. 244), has received, as I have said, 

 the name of the distinguished investigator to 

 whose labors we owe much of our present knowl- 

 edge of these animals. Let us look now at an- 

 other group of Hydroids, whose mode of develop- 

 ment is equally curious and interesting. 



The little transparent embryos from which they 

 arise, oval in form, with a slight, scarcely percep- 

 tible depression at one end, resemble the embryos 

 of Coryne already described. They may be seen 

 in great numbers in the autumn, floating about in 

 the water, or rather swimming, — for the motion 

 of all Radiates in their earliest stage of existence 

 js rapid and constant, in consequence of the vi 



* See wood-cut, p. 239 



