ECHINODERM LARV^. 473 



figures the four-weeks-old bipinnaria stage of the larva 

 of Asterias glacialis, which he had reared from artificially- 

 fertilised eggs in the Plymouth Laboratory. This figure 

 enables me to identify the bipinnaria represented in 

 fig. 10, PL I, which was captured in a tow-netting in 

 Port Erin Bay in April, 1911, and is, I doubt not, the 

 larva of Asterias glacialis. A number of specimens of 

 this larva were found in every haul of the tow-net taken 

 at the end of March, and it was still fairly common at 

 at the time of going to press (April 20th, 1914). Its 

 occurrence in previous years was rare. The only 

 essential difference between the specimen figured by 

 Mortensen and that from Port Erin lies in the disposition 

 of the ciliated band, which may be accounted for by 

 assuming a slight difference in age. In both larvae the 

 right and left coelomic vesicles had grown forward and 

 united in the pre-oral lobe. Mortensen does not figure 

 any communication of the left vesicle with the exterior 

 through a pore-canal and water-pore, and I also was 

 unable to find any trace of these structures in the Port 

 Erin specimen. 



I am again indebted to Mortensen's paper for help in 

 identifying the larva represented from the left side in 

 fig. 11, and from the ventral face in fig. 12, PL II. It 

 occurred in very small numbers in the plankton in June 

 and July, from 1905 to 1909 inclusive, but like some 

 other Echinoderm larvae has not come under observation 

 during the past four years. It is the larva of Luidia 

 ciliaris. Mortensen reared this larva also from artificially 

 fertilised eggs. The specimens from which my figures 

 were drawn were older than the five-weeks-old one figured 

 by Mortensen, inasmuch as in the former the arm-like 

 processes characteristic of the brachiolaria have attained 

 some length, while in the latter they have scarcely begun 



