EMBKYOLOGY AND CLASSIFICATION. 305 



the other are superior to those with circular out- 

 lines. The Maiiicina, 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 Astraea 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 Ctenophora3, 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 



