6-946 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 
‘S rapid and constant, in consequence of the vi 
* See wood-cut, p. 239 
