ECHINODEEM LARV^. 475 



first acquaintance with this interesting larva was made 

 so long ago as May, 1892, when, in a tow-netting, I took 

 a specimen which had reached the stage of development 

 represented in fig. IT. At that time I felt confident that 

 the five-rayed structure which came into view when the 

 specimen had been mounted in balsam was a hydrocoel, 

 and that the organism would prove to be the larva of an 

 Asterid. I was led to refer it to Solaster by seeing an 

 adult specimen of S. papposus extrude a number of com- 

 paratively large, orange-coloured eggs in the Aquarium 

 of the Port Erin Biological Station. Its identity has now 

 been established beyond doubt by Gemmill. The larva of 

 Solaster occurs in the plankton of Port Erin Bay in small 

 numbers in April and May. Its bright orange colour, 

 contrasted with the dull green of the vernal phyto- 

 plankton with which it is usually associated, makes it a 

 conspicuous object in plankton gatherings. In the paper 

 cited above, Gemmill states that many of the larvae of 

 Solaster endeca which he collected by means of the tow- 

 net in the neighbourhood of Millport, " showed minor 

 abnormalities of growth," and from this circumstance he 

 infers that it is " chiefly unhealthy larvae which come to 

 the surface of the sea. They are soft and readily break 

 up against the cloth of a tow-net." My own experience 

 accords with this ; but I have obtained from plankton 

 gatherings in successive years a number of these larvae 

 in various progressive stages, from the segmenting egg 

 to that in which metamorphosis is nearly complete 

 (fig. 18). It is noteworthy that even at this late stage 

 of development, of which I have seen only one example, 

 the larva is still five-rayed. Gemmill gives an account 

 of the mode in which it attains the many-rayed condition 

 of the adult. Owing to the opacity of the orange pig- 

 ment, it is not possible to make out the position and 



