SUCCESSION AND DEVELOPMENT OF ANIMALS. 171 



pean Comatula alone was known. (See Sect. XVIII, p. 105.) 

 This had already shown that the early stages of growth 

 of this Echinoclerm exemplify the pedunculated Crinoids 

 of past ages. I have myself further seen that the succes- 

 sive stages of the embryonic growth of Comatula typify, 

 as it were, the principal forms of Crinoids which charac- 

 terize the successive geological formations. First, it recalls 

 the Cistoids of the palaeozoic rocks, which are represented 

 in its simple sphseroidal head, next the few-plated Platy- 

 crinoids of the Carboniferous period, next the Pentacri- 

 noids of the Lias and Oolite with their whorls of cirrhi, 

 and finally, when freed from its stem, it stands as the 

 highest Crinoid, as the prominent type of the family, in 

 the present period. The investigations of Mttllcr upon 

 the larvse of all the families of living Asterioids and Echi- 

 noids enable us to extend these comparisons to the higher 

 Echinoderms also. The first point which strikes the 

 observer in the facts ascertained by Muller is the extra- 

 ordinary similarity of so many larvae of such different 

 orders and different families as the Ophiuroids and Aste- 

 rioids, the Echinoids proper and the Spatangoids, and 

 even the Holothurioids, all of which end, of course, in re- 

 producing their typical peculiarities. Secondly, it is very 

 remarkable that the more advanced larval state of Echi- 

 noids and Spatangoids should continue to show such great 

 similarity that a young Amphidetus hardly differs from a 

 young Echinus. 1 Finally, not to extend these remarks 

 too far, I would only add that these young Echinoids 

 (Spatangus as well as Echinus proper) have a general re- 

 semblance to Cidaris, on account of their large spines, 

 rather than to Echinus proper. Now, these facts agree 



1 Compare J. Midler's 1st paper, pi. Ill, with pis. IV- VII, and with pis. 

 VI aud VII, 4th paper. 



