284 



THE CANADIAN NATURALIST. 



[Sept. 



(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 Cadaster, says, " From the construc- 

 tion of these striatious on the face of Cadaster, 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 specimens, 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 interposition 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 (c c, figs. 4, 5,) 

 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. 



Fig. 4. Hydrospire of Caryocrinus ornatus. a, surface view; the dots 

 around the margin are the spiracles, the small dotted lines represent 

 the course of the flat internal canals ; c,c, suture between the two 

 plates ; b, transverse section. 5. Hydrospire of pleurocystites. a, 

 surface view : c,c, suture ; 6, transverse section. 6, The same with 

 the points, c,c, drawn together. 7. Internal gill of a spider. 



