64 



S. LOVEN, ON POURTALESIA, A GENUS OF EOHINOIDEA. 



as typically composed of a central ossicle, five costals, and five radials. ^) I shall make 

 use of the same terms here, without fear of being misunderstood. When future seience 

 shall liave lying before lier, for comparison, nuiuerous forms now undiscovered, and the 

 perplexities of the present shall have cleared up, the final terminology Avill come of 

 itself. -) 



What the calyx is to the antique Crinoid, its homologon is not to the Echinoid, 

 — its constituents were inherited raorphologically, not their modes of snbserviency 

 to the physiological activities of the animal — ; along with the enormous change in 

 conditions of existence there have arisen essential alterations of the entire strncture. 

 In the Crinoid, as in the Echinoid, the calyx is normally opposite to the mouth. In 

 the stalked Crinoid, which feeds by raeans of ciliar}' agency, the mouth is directed 

 upwards, and the calyx, on the darkened side, is the fundamental support on which 

 the body rests, periuanently or temporarily, enclosed on all sides by its perisome, 

 with its radiating grooves. In the Echinoid, when first seen by us already long since 

 adapted to a free and ground-feeding life, with the mouth directed downwards, the 

 calj^cinal system, permanently adnate, is carried uppermost, towards the light, on the 

 top of the back, and there, covering probably the dorsal part of the perisome, nor- 



xmy 



Cyathocriuus alntaceus 

 Ang. 



Tiarechinua princepa 

 Laube. 



Salenia sp. 



Echinus sp, youug. 



Cidaris Merceyi 



COTTEAU. 



mally meets the ambulacra radiating from the mouth, at their groAving extremities, 

 but never lifts or supports them. ') In consequence of the thus inverted posture, 

 the inner organs of the Echinoid are to a great extent transposed and brought iu- 

 to relations to the calycinal system Avidely contrasting with those existing in the 

 Crinoid. Relatively to the other skeletal constituents the calyx holds its legitimate 

 position, but under it, OAving to altered conditions, an assemblage is brought together 

 of organs of primary importance: those of vision, — apparently foreign to the Crinoi- 

 dean type, at least not to be looked for in a homologous place — , those of generation, 

 of aqueous circulation, and of excretion. And tluis, in the Echinoid, the calycinal system 

 is rendered, to no small extent, a disputed ground, each of these organs tending to 

 penetrate its substance, and to gain access to the surrounding Avater. 



Of all the Echinoidea at present knoAvn Tiarechinus has the most antique looking 

 calycinal system, Pl. XIII. It is large enough to cover the greater part of the dorsal 



') Études p. 73. 



-) It is well known that Miller was incnnsisteiit in the use of the term "costals», l)ut it hns alvvays been 



considered allowable to suggest the use in a strict sense of a term elsewliere vaguely applied. 

 =*) Études, 1. c. 



