484 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



by the cap of deeply-staining cells at the posterior apex 

 of the body. A full-grown larva, the specimen captured 

 by Mortensen had not entered upon its metamorphosis. 

 In Gravely's specimen all the primary elements of the 

 skeleton of the adult are present (fig. 45). Figure 44, 

 drawn under a low power, shows the five terminal plates 

 (tl.), three dorsal and two ventral, which have already 

 assumed the characteristic basket-like form of these 

 plates, and project as slight eminences from the general 

 surface of the body. Figure 45, drawn under a higher 

 power, shows the three of these plates which lie upon the 

 dorsal face of the body and are visible in one and the 

 same focal plane. The madreporic plate (7n.pl.) overlies 

 the hydrocoel (hy.), which has moved some distance for- 

 ward along the oesophagus preparatory to encircling that 

 organ. On the right side of the body the central (en.) 

 and three of the radial plates (rl.) are shown. 



There remains to be mentioned only one Ophiuroid 

 larva; and, owing to the fact that I have seen only two 

 or three of the latest stages of the metamorphosis and no 

 growing plutei, I cannot describe it in detail. Figure 

 46, PL YII, was drawn from one of several specimens 

 found in the plankton in December, in which month alone 

 this larva has hitherto occurred in successive years. It 

 was carefully searched for, but not seen in 1913. In this 

 the central, radial and terminal plates have taken up their 

 respective positions in the disc of the future Ophiuroid. 

 Of the pluteus only the postero-lateral arms remain ; but 

 the form of the proximal ends of the skeletal rods of these 

 and of the posterior and transverse rods is sufficient to 

 indicate the specific distinctness of this larva from those 

 described above. On one occasion I had the good fortune 

 to see the post-larva (fig. 47) free itself from the remains 

 of the pluteus and move about actively by means of its 



