262 ALTERNATE GENERATIONS. 
there are many others resembling these in all 
the essential features of their-structure, but dif- 
fering in their mode of development; for, al- 
though more or less Polyp-like when first born 
from the egg, they never become attached, nor 
do they ever bud or divide, but reach their mature 
condition without any such striking metamor- 
phoses as those that characterize the develop- 
ment of the Hydroid Acalephs. All the Meduse, 
whether they arise from buds on the Hydroid 
stock, like the Sarsia, or from transverse division 
of the Hydroid form, like the Aurelia, or grow 
directly from the egg to maturity, without paus- 
ing in the Hydroid phase, like the Campanella, 
agree in the general division and relation of 
parts. All have a central cavity, from which 
arise radiating tubes extending to the margin 
of the umbrella-like disk, where they unite either 
in a net-work of meshes or in a single circular 
tube. But there is a great difference in the 
oral apparatus; the elaborate ruffled curtains, 
that hang from the corners of the mouth, occur 
only in the Species arising from the transverse 
division of the Polyp-like young. For this rea- 
son they are divided into two Orders,—the Hy- 
droids and the Discophora. __ 
The third order, the Ctenophore, are among 
the most beautiful of the Acalephs. I have spo- 
ken of the various hues they assume when in 
