ECHINODEEMA. 193 



radially disposed buds separate from one another to a certain ex- 

 tent, without however ever becoming completely separated ; so that 

 a number of organs, or separate portions of organic systems, are 

 common to them all. In this way the budding individuals remain 

 connected as a single organism, and losing their individuality, 

 sink to the level of mere parts only of a body (antimera). 



This hypothesis of the derivation of the Echiuoderma from the 

 Vermes leads us to classify the former above the latter, for we 

 suppose that the Vermes gave the starting-point for the development 

 of the Echiuoderma. 



The separate divisions of the Echiuoderma (Star-fishes) are thus 

 arranged : 



I. Asteroida (Sea-stars).* 

 Asterida. 



Asteraoanthion, Solaster, Asti'opectsn, Luidia. 



Brisingida. 



Brisinga. 



Ophiurida, 



Ophioderma, Ophiolepis, Oplaiothris, Ophiocoma. 



Euryalida. 



Astrophyton. 



II. Crinoida ^Lily-stars). 

 Brachiata. 



Pentacrinus, Comatula. 



III. Echinoida (Sea-urchins). 



Demosticha. 



Bchinothurida.t 



Calveria, Phormosoma. 

 Cidarida. 



Cidaris. 

 Echinida. 



Echinus, Eohinometra. 



Petalosticha. 



Spatangida. 



Spatangus. 

 Clypeastrida. 



Clyjieaster, Laganum, Scutella. 



IV. Holothuroida (Sea-cucumbers). 



Eupodia. 



Holotlmria, Molpadia, Pentacta, Psolus, Cuvieria. 



Apodia. 



Synapta, Chirodota. 



_ * The Asteroida must be put first, as including the oldest Echinoderma, and as 

 being the nearest in organisation to the hypothetical stem form. Among the fossil 

 forms of this group we find conditions which are allied to those of the next class 

 (Crino'ida) . 



t This most important family presents points of connection with the Asterida; 

 notably in the possession of a movable dermal skeleton. 



