ON THE DEVELOPMENT OF SOME BRITISH ECHINODERMS. 5 



papillae, while in the two other species there are only 2-3 papillae at each 

 side of it (cp. text Figs. 4-6 of Delage's paper). Also the crown of the 

 brachiolarian processes appears to afford a good specific character, there 

 being 2-3 circles of small papillae on a thickened ring, while in the other 

 species there is only a single circle of papillae at the tip and no thickened 

 ring. If this proves to hold good for the normally developed larva of 

 A. glacialis, it will be easily distinguishable from the other species. A 

 number of larvae which were taken in the Plankton at Plymouth all had 

 only 2-3 papillae at each side of the disc, and the crowns consisting of a 

 single circle of papillae ; they should accordingly all belong to A. ruhens^ 

 which may be possible, since also some few ripe specimens of this species 

 were found. In any case, it is very desirable to have the A. glacialis 

 larva reared to its full size, so that we may be able to see, with certainty, 

 by which characters it differs from the A . rubens and A . vulgaris larvae. As 

 the species A. glacialis is not so very closely related to the other two species 

 mentioned, one would expect the larvae likewise to be distinct enough. 



In the Echinodermenlarven der PlanMon Expeditioti (p. 43), I have 

 distinguished, under the name of Bipinnaria Icevis, an Asterias larva 

 found by Joh. Mliller at Elsinore, which differs from the A. rubens larva 

 in having no dorsal median process. I suggested that this larva might 

 belong to A. glacialis, as there are found only three Asterias species in 

 the Sound (between the Kattegat and Baltic), i.e. A. rubens, Mulleri and 

 glacialis, the latter being, however, very rare here. The larvae reared by 

 Delage would seem to show that the dorsal median process is as well 

 developed in the Bipinnaria of A. glacialis as in those of A. rubens 

 and vulgaris, and then the B. Icevis can only be an abnormal larva of 

 A. rubens. I have never observed such specimens among the numerous 

 larvae of this species which I have seen. 



The culture of the A. glacialis larvae showed the interesting feature 

 that a large number of the larvae, about 50 per cent of them, had either 

 two dorsal pores, one for each enteroccel vesicle, or the vesicles were 

 united across the stomach, having one single, median pore (Figures 5-6), 

 This feature has also been observed by Goette* in the larva of the same 

 species, (jr. W. Field, in his paper "The Larva of Asterias vulgaris'" f 

 (pp. 110-111), describes the formation of two pore canals in the young 

 A. vulgaris larva as a normal feature, while the presence of two pore 

 canals has otherwise been regarded as pathological. Field found the two 



* Goette, " Bemerkungeu ziir Entwicklungsgeschichte der Echinodermen '' {Zool. An- 

 zeiger, 1880, p. 324. Fig. 2). 



t Quarf. Jonrn. Micr. Sci., N.S., 3t, 1803. 



