MONOGRAPH OF THE EXISTING CRINOIDS. 513 



ectoderm appeared as an epithelium sharply marked off interiorly; elsewhere it 

 was so intimately united with the mesenchyme that the two together formed a 

 uniform tissue. The coelomic sacs showed no noteworthy deviations from the nor- 

 mal. On the ventral side there were nine tentacles which showed the same structure 

 as those in the larvse just described. These nine tentacles represented the three 

 posterior groups of evaginations from the hydrocrele, the two anterior groups being 

 so slightly developed that the body surface on the left side appeared entirely 

 smooth, while that on the right side showed such small projections that they could 

 not appropriately be referred to as tentacles. Larvse such as these appear to be 

 incapable of further development. 



Sir Wyville Thomson noticed that when the ova are liberally supplied with 

 fresh sea water and placed in a warm temperature the later stages of larval growth 

 are, as it were, hurried over, so that the free larvae scarcely attain their perfect 

 form before being distorted by the growing crinoid. In other instances, in colder 

 seasons and in a less favorable medium, the larvte reach a much higher degree of 

 independent development and retain for a longer period the larval form. 



W. B. Carpenter remarked that the embryos when losing the power of locomo- 

 tion were frequently seen floating in such a manner that the incipient discoidal 

 base spread itself out (often in a stellate form) on the surface of the water, while 

 the column and body of the rudimentary pentacrinoid hung downward from this ; 

 and it sometimes happened that by the approximation of a number of individuals 

 in the same condition the stellate extensions of the disks became mutually adherent. 



In a 48-hour larva Seeliger found six basal instead of the normal five ; two of 

 the six were considerably smaller than the other four, and evidently together rep- 

 resented the normal fifth. 



THE PENTACRINOID YOUNG. 

 COMISSIA LITTORALIS. 



On one of the specimens of this species collected by the naturalists of the 

 Siboga on a reef near the anchorage off the Kawio and Kamboling Islands, Kar- 

 karalong group, on July 22-23, 1899, there were a number of pentacrinoids attached 

 to the cirri. The smallest of these has apparently just attained the erect position. 

 The others resemble very closely the pentacrinoids of Comactinia meridionalis. 



One of them measures 2.2 mm. in total length, the crown being 0.6 mm. long. 



The stem is composed of 13 columnals of which the first four are very short 

 and lenticular, the fifth nearly twice as long as broad, the sixth longer, and the 

 seventh and eighth the longest, nearly four times as long as broad. 



The terminal stem plate is circular. 



The radials are about the same size as the basals, approximately square with 

 rounded angles, just in apposition laterally. The IBr x and IBr.,, which are 

 extraordinarily narrow, are present. 



The radianal lies on the left distal edge of the right posterior radial, which 

 is broadly cut away for its reception, though its left lateral angle almost reaches 

 the right lateral angle of the left posterior radial; the radianal reaches about 

 to the posterior interradial suture, and distally to just beyond the base of the 



