ECHIXODEEMATA. 47 



Notwithstanding, the anatomy, especially of the water- vascular 

 system, is very complex. 



Keproduction is sometimes direct, but a bilateral planula, it is 

 said, generally emerges from the egg. Synapta has a form of 

 larva known as " Auricularia." 



The "Cuvierian organs" are thread-like tubes and fibres open- 

 ing into the cloaca, or into the water- vascular system. 



No fossil species are known ; a few of their calcareous spicules 

 have been found in the Carboniferous deposits. 



Glaus has two orders Pedata and Apoda : the first with two 

 families Aspidochirotae (Holothuria, &c.) and Dendrochirotae 

 (Psolus, &c.) ; the second order contains the two families Molpa- 

 didas (constituting his suborder Pneumonophora) and Synaptidaj. 



Without organs of respiration APNEUMONA. 



With organs of respiration PNEUMONOPHORA. 



Order I. APNEUMONA. 



No special organ of respiration. Hermaphrodite. No Cuvierian 

 organs. 



There are no ambulacral feet in Synaptidae ; but locomotion is 

 effected by the spicules, which are anchor-shaped, barbed, wheel- 

 shaped, &c., according to the .genera. In Oncinolabidae the tube- 

 feet are in five rows and the tentacles are filiform. 



Chirodota. Oncinolabidte. 



Synapta. Eupyrgus. Oncinolabes. 



Myriotrochus. Anapta. Echinosoma. 



Order II. PNEUMONOPHORA. 



DlPNEUMONA. 



Respiratory organs branching, tree-like, opening into the cloaca. 

 Sexes distinct. Cuvierian organs present. 



Water is admitted into the abdominal cavity by means of the 

 respiratory organs : these are two in number, except in Rhopa- 

 lodina. Molpadiidae have no tube-feet ; they are doubtfully 

 hermaphrodite. The tentacles are either shield-shaped [Aspido- 

 chirotoe=:Holothuriidce] or branched [Dendrochirotse PsoLidae]. 

 In Molpadiidaa the tentacles are either cylindrical or shield- 

 shaped. Bhopalodina has a flask-shaped body, the mouth at the 



