72 EMBRYOLOGY OF THE STARFISH. 



berylinvis and Asteracanthion pallidus — species which have their representa- 

 tives in Europe, and which have, up to the present time, been included in 

 the same genus with Asteracanthion Miilleri — are free-swimming larvae, 

 resembling the Bipinnaria of Miiller. These facts can, therefore, leave but 

 little doubt that MuUer and Van Beneden have observed the larvae of 

 Asteracanthion rubens M. T., and of allied species, the larv^ of which 

 have been called by them Bipinnaria, Bi-achiolaria, and Brachina, and are 

 only different stages of one and the same generic type. The difference of 

 the two modes of development of A. Mulleri and A. pallidus is so great, 

 that these two groups of species have been separated into two genera by 

 Professor Agassiz. [Verrill has subsequently placed A. Mulleri in a sejoarate 

 genus (Leptasterias), to which have been added Asterias tenera and A, 

 compta. The former is probably what I have seen called A. flaccida. See 

 also Memoirs Am. Acad. Fifi. 34, 1864, for an account of its mode of de- 

 velopment. Compare also tlie development of Pteraster militaris, M. Sars, 

 Norges Echinodermer, 1861. (PI. VI. Figs. 3-13).] The Brachiolaria from 

 Trieste and Messina present very striking differences from the northern 

 Brachiolaria. These larvae are probably the young of Asterias tenui- 

 spinus, so common in the Mediterranean. In his revision of the Starfishes, 

 Professor Agassiz has also separated this species from the true Asteracan- 

 thion, under another generic name. We have next the Bipinnaria asteri- 

 gera, still another type of larva, belonging in all probability to another 

 family, differing from both the other larval forms. As Bipinnaria asteri- 

 gera can only be the larva of a Pteraster, a Ctenodiscus, an Astropecten, 

 or of an Hippasteria, either of which belong to families distinct from the 

 Brachiolaria type of larvae, we find differences in form, modified by struc- 

 tui'al features, characterizing the larval conditions, as well as the adult 

 stages of families of the same order ; while structural peculiarities in the 

 larvae characterize the different generic divisions more plainly than in the 

 more advanced conditions. It is evident, from the observations of Pro- 

 fessor Agassiz and of Sars, that the Asterias violaceus of Thomson, the 

 embryology of which he has traced in the Microscopical Journal, must 

 be placed in the same genus with A. Mulleri, and may, perhaps, be iden- 

 tical with it, unless the true A. violaceus L. has also a similar mode of 

 development. [This would most certainly prove that A. violaceus, at least 

 what the English call A. violaceus, cannot be the male of the European 

 of A. rubens, as has been suggested by several European writers on Star- 



