DIFFEEENT TYPES OF LARViE. 71 



fill examination of the position of the Starfish in the Bii)innaria asterigera 

 with the mode of development as noticed in Echinaster (Crihrelhi) A. flac- 

 cida, and A. Mullen, will give the means of settling the true affinities of the 

 singular ventral appendage of these larvae, and of deciding whether they 

 are, as I have suggested, the homologues of the brachiolar appendages, — 

 a result which seems probable from the observations made by Professor 

 Agassiz, of a circulation in this peduncle, in a species of Asterias (A. flac- 

 cida, Afj.) closely allied to Asteracanthion Miilleri, the mode of develop- 

 ment of which is identical with that observed by Sars in Echinaster. 



Professor Thomson, who has had occasion to study the sedentary mode 

 of development of several Echinoderms, has given us the most accurate 

 description of the structure of this peduncle, in a species Avhich he calls 

 Asterias violaceus. A glance at his figures and descriptions will suffice 

 to show us the complete identity between the brachiolar appendages and 

 this peduncle, in which there is a circulation arising from a branch of the 

 water-tube, and at the base of which, at the point of junction of the three 

 arms, we find a peculiar disk, having the same structure as the elliptical 

 disk, noticed at the base of the brachiolar arms in our Starfish larv*. But 

 we cannot agree with Professor Thomson, that this peduncle is the first 

 sign of an ambulacral tentacle, the ambulacral tentacles being developed 

 at a totally different part of the water-tube* 



JDiferent Types of Larvcv. — Miiller did not suspect that his Bipinnaria 

 and Brachiolaria were the larva) of different species of Asteracanthion. 

 The observations of Sars, who had traced the embryology of Asteracan- 

 thion Miilleri, in which the eggs attain their full development without 

 leaving the mouth of the parent, seemed to preclude the possibility of 

 these nomadic larvoe belonging to the same genus. He even went so far 

 as to say that his Bipinnarioe belonged to the same genus as the Starfish 

 of the Bipinnaria asterigera. This is undoubtedly an env.r, for the Star- 

 fish of the Bipinnaria asterigera, as figured by Miiller, and by Koren and 

 Danielssen, has already the characters of a Pteraster ; and it is evident 

 that the Bipinnaria of Miiller, being a young Brachiolaria, which 1 have 

 shown to be the larva of an Asteracanthion, cannot belong to that 

 genus. 



The larvae which I raised by artificial fecundation from Asteracanthion 



* [See also a most interesting paper by Thomson in the Journal of the Linna\»n Scnietv, ^ ol. XIII. 

 p. 57, 1876.] 



