EMBRYOLOGY AND CLASSIFICATION. 305 
the other are superior to those with circular out- 
lines. The Manicina, with its convoluted trench- 
es, is, in its earlier condition, a perfectly cir- 
cular hydra-like simple Polyp; and the young 
Herpolitha is also a simple circular animal, so 
closely resembling a young Fungia that it 
might be referred to the same genus. I have 
no doubt that, when the embryonic history 
of the young Madrepore is fully understood, it 
will be found that this group also resembles the 
young Astrea at first, though it stands so much 
above it in its adult condition. In truth, all 
these higher representatives of the class of Polyps 
resemble the lower ones in their earliest state, 
starting from a point common to all, and passing 
through phases which are permanent and final 
for the lower forms, but are only transient stages 
in the development of the higher ones. 
I have dwelt so much upon the Embryology of 
the Acalephs in another chapter, that I need only 
remind my readers here that this class also has a 
common starting-point, exhibiting a remarkable 
uniformity among the young, which extends even 
to the Ctenophore, the affinities of which have 
been, and still are, the subject of controversy 
among naturalists. In this class also, the differ- 
ent phases of development furnish the best basis 
for a classification of its representatives. 
Until very recently it had been believed that 
T 
