96 



2. On the pectinated rJiomhs and calycine 2)ores of the Cystidea. 



None of the organs of the Echinodermata have been the subject of so 

 much speculation as the caljcrae pores and the so-called " pectinated 

 rhombs " of the Cystidea. Their relations and function long remained in 

 doubt, but there seems to be, now, sufficient data to show that they are 

 respiratory organs, and also, that they are the homologues of the tubular 

 apparatus which underlies the ambulacra of the Blastoidea. J. Muller 

 suggested a comparison between these peculiar organs and the respiratory 

 pores of the Asteridce. (Uber den bau der Echinodermen, p. 63, 1853.) 

 Prof. Huxley has placed them in the same relation. (Medical Times, 

 Dec, 1856.) Eichwald calls them respiratory pores. (Lethaea 

 Rossica, vol. 1, p. 614, 1860.) Prof. Dana says " they are probably 

 connected with an aquiferous system and respiration. (Man. Geol., p. 

 162, 1863.) Mr. Rofe, after showing that their structure is the same 

 as that of the striated surfaces between the rays of Codaster, says,. 



from the construction of these striations on the face of Codaster, and 

 on the 'pectinated rhombs ' of the cystidea, may we without assumption 

 suggest the possibility of their being respiratory sacs, lined with cilia, and 

 constructed of a porous test, through which air from the water could pass 

 by diffusion." (Geol. Mag., vol. ii, 251, 1865.) As for myself, when 

 I prepared my decade on the cystidea, I gave this subject a great deal 

 of consideration, and studied a large number of specmiens, but could 

 arrive at no conclusion satisfactory to myself I am now convinced that 

 the view of the above named distinguished authors is the correct one. 

 These are respiratory organs. In all the species in which they occur, 

 they seem to be constructed on the same general plan, i. e., the interpo- 

 sition of an exceedingly thin partition, between the circumambient water, 

 and the fluid within the general cavity of the body. They are usually of 

 a rhomboidal shape — each rhomb being divided into two triangles by the 

 suture (<?, figs, 53, 54,) between two of the plates. In several of the 

 genera the two halves of the hydrospires are reniform, ovate or lunate, 

 and either internal or external. 



In order to avoid the use of double terms, I propose to call them 

 " hydrospires,^^ and their apertures, pores,^'' fissures, or spiracles 

 according to their form. 



In Caryocriniis ornatus the hydrospires (fig. 53,) are of a rhomboidal 

 form, and have each of the four sides bordered by a single row of small 

 tubercles. Some of these tubercles have a single pore in the summit, 

 while others are perforated with a variable number, — from two to twenty, 

 or perhaps more, — thus becoming vesicular or spongy. It is only the 

 apex of the tubercle, however, that has this structure, for, when this is. 



