ECHINODEKMATA. 222 



scribed by their discoverer*, to whom also we owe the subsequent! j 

 acquired knowledge of their metamorphoses, as a new species of 

 Pentacrinus (P. £uropceus). These small Pentacrines entirely dis- 

 appear in September, at which season the young Comatulse make 

 their appearance : but the actual metamorphosis of the Pentacrine 

 into the Comatule has not yet been seen. The latter we know 

 enters life as an active ciliated larva ; it next selects a suitable 

 situation for its sedentary pentacrinite stage of existence ; and 

 analogy plainly indicates that the crinoid capital, dropping from the 

 stalk by an act of transverse fission, becomes the Comatula, which 

 thus a second time assumes a free condition of existence under its 

 mature form. Nor are these metamorphoses a whit more extra- 

 ordinary than those of the gelatinous Medusas : nay, the parallel 

 would be extremly close, since we saw that the Cyanaea entered life 

 as a ciliated locomotive infusory, then became a sedentary polype, 

 supported on a central stem, which finally resolved itself into freely 

 swimming aclephans by several transverse fissions. Other highly 

 interesting considerations arise out of the predominance of the 

 Crinoid forms over the Asteroids, and of the Cystideoids over the 

 Echinoids in the secondary and palaeozoic formations respectively ; 

 for the Crinoids would seem to be not the only representatives of the 

 larvae of actual species, if the bold conjecture of Prof. Ed. Forbes be 

 true, that the pectinated rhombs of the more ancient Cystidese answer 

 to the ciliated "epaulettes" of the Pluteus^i for in that case the 

 pedunculated Cystidese would, as old permanent forms of Echinus- 

 larvae, represent the Crinoids in the family Echinidae. 



As we advance in our sui'vey of the organization and metamor- 

 phoses of animals, we shall meet with many examples, in which the 

 embryonic forms and conditions of structure of existing species have 

 at former periods been persistent and common, and represented by 

 mature and procreative species, sometimes upon a gigantic scale.:^ 



Summary of the Orders and Families of the 



Class ECHINODEKMATA. 



Marine, commonly free, repent animals, with the integument, in 

 most, perforated by erectile tubular tentacles, hardened by a reticulate 

 deposit of calcareous salts, and, in many, armed with spines. A vas- 



* CLVm. t CLXXIX. vol. ii. p. 184. 



I LXXXIV. (1843), p. 129. V. Baer rightly characterised the course of de- 

 velopment of an individual animal as " a passage from a more general to a more 

 special type." But, in substituting this mode of expressing the idea broached in 

 the text, the modifier of the phraseology seems scarcely justified in claiming that 

 idea as " particularly his own." See IV. (1851), p. viiL 



