

230 PROCEEDINGS OF THE ACADEMY OF [1819. 



groups, and this may perhaps explain in a measure the compara- 

 tively large size of the eatyx in the older Crinoids generally. The 

 hydrospires were located within the perivisceral cavity, connected 

 with the inner floor of the test, and communicated, so far as ascer : 

 tained, through the test witli the outside water. In the Cystideans 

 the hydrospires are of a rhomboidal shape each rhomb being 

 divided into two triangles by a suture between two of the plates 

 (PI. 17, Figs. 7, 8.). In Caryocrinus ornatus, each of the four sides 

 of the rhombs 4s bordered bj r a row of small tubercles (PI. 17, Fig. 

 6), some of which have a single pore in the apex, while others are 

 perforated by two to twenty or more. The pores penetrate through 

 the plates, but do not communicate directly with the visceral cavity 

 of the body. Internally, each hydrospire consists of a number of 

 flattened tubes, arranged parallel to each other, and each tube re- 

 ceives two of the pores, one at each end. In a large hydrospire, 

 there are about twenty or more tubes. Whatever may have been 

 the special function of these tubes, naturalists generally agree 

 that they belong to the respiratory sj'stem, and we infer from the 

 distribution of the pores in variable numbers at and about the 

 apices of the tubercles, that they very probably served as a madre- 

 poric apparatus, through which water for respiration was intro- 

 duced and expelled. In other genera of the Cystideans, we find 

 in the test one or more striated rhombs with fissures and pores, 

 somewhat resembling the madreporic body of other Echinoderms. 

 In the Blastoids, there are certain orifices arranged around the 

 actinal pole, which have been called ovarian apertures on account 

 of their supposed resemblance to similar openings in the Ophiu- 

 rans, but if they were connected with the reproductive organs, 

 which is by no means proved, they evidently had additional im- 

 portant functions. These openings appear in various forms. We 

 find in the earlier t} r pes fissures arranged on the upper portion of 

 the body ; at a later period slits along each side of the ambulacra, 

 and in the latest and higher types, five pairs of orifices which 

 surround the oral centre. None of these openings communicate 

 with the general cavity of the body, but they all connect with 

 peculiar organs closely resembling the internal tubes of Caryo- 

 crinus, and which are also called " hydrospires." The hydrospires 

 of the Blastoids, though actually arranged interradially, are 

 located beneath the ambulacra, and occupy the perivisceral cavity, 

 extending laterally for some distance beyond the sinus along the 



