476 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



relations of the coelomic and other internal structures in 

 the living larva. All the specimens from which figs. 14 to 

 19 were drawn were lightly stained in horax carmine, and 

 mounted without pressure in balsam. 



Larvae of Ophiuroidea. 



Seven species of Ophiuroidea have been found in the 

 neighbourhood of Port Erin, and Gravely and I have 

 distinguished eight ophioplutei, which occur more or less 

 abundantly in the plankton of the bay. The larva of one 

 species, Amphiura elegans, is, however, not pelagic; so 

 that it is probable that two of the ophioplutei represent 

 species which either have not yet been discovered in the 

 district or occur in the deeper waters outside its limits. 



The species to which I would first draw attention is 

 one to which Mortensen (12) has given the temporary 

 name "mancus." It occurred in considerable numbers, 

 along with the species to be next described, in July, 1907, 

 and 1908, respectively, and is easily recognised; the 

 postero-lateral arms being gracefully curved, and the 

 skeletal rods which support them bearing slightly curved 

 spine-like projections at tolerably regular intervals along 

 their inner sides, as shown in fig. 20, PI. III. The 

 tips of these arms, as well as the posterior end of the 

 body, are tinged with orange or red pigment. Gravely 

 and I found this species a favourable one for the study 

 of the main features of the development of the coelomic 

 vesicles, especially the hydrocoel, and of the primary 

 elements of the skeleton of the adult. It is practically 

 free from the dark pigment which so much obscures 

 structural detail in the pluteus of Ophiothrix fragilis. 

 Fig. 22 is a ventral view of a young pluteus in which the 

 right and left coelomic vesicles have just divided into 



