58 EMBRYOLOGY OF THE STARFISH. Part I. 



and of the madreporic body. The slit in the Starfish, noticed by Midler and 

 Koren and Danielssen, was probably owing to the fact that in their young speci- 

 mens the spiral was not yet closed and flattened, as is the case in older Starfishes. 



From the drawings of Sars, and of Koren and Danielssen, it would seem as if 

 a large tube extended into the long appendage opposite the arms. If this is 

 truly so, it leaves no doubt that the long, tail-like appendage of the Bipinnaria is 

 homologous to the brachiolar appendages of our larvse, only developed to a much 

 greater extent, and with all the arms placed nearer together, immediately round the 

 mouth. A comparison, after careful examination of the position of the Starfish in 

 the Bipinnaria asterigera, with the mode of development as noticed in Echinaster 

 (Cribrella) A. flaccida, and A. Mulleri, will be 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. flaccida, Ag.) closely allied to Asteracanthion 

 Mulleri, the mode of development of which is identical with that observed by Sars. 



Professor Thompson, who has had occasion to study the sedentary mode of devel- 

 opment of several Echinoderms, has given us the most accurate description of the 

 structure of this peduncle, in a species which 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 ellipti- 

 cal disk, noticed at the base of the brachiolar arms in our Starfish larvas. But we 

 cannot agree with Professor Thompson, 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. 



Different Types of Larvae. — Muller did not suspect that his Bipinnaria and Brachi- 

 olaria were the larvse of different species of Asteracanthion. The observations of 

 Sars, who had traced the embryology of Asteracanthion Miilleri, in which the eggs 

 attain their full development without leaving the mouth of the parent, seemed to 

 preclude the possibility of these nomadic larvas belonging to the same genus. He 

 even went so far as to say that his Bipinnarise belonged to the same genus as the 

 Starfish of the Bipinnaria asterigera. This is undoubtedly an error, for the Starfish 

 of the Bipinnaria asterigera, as figured by Muller, and by Koren and Danielssen, has 

 already the characters of a Pteraster; and it is evident that the Bipinnaria of Muller, 

 being a young Brachiolaria, which I have shown to be the larva of an Asteracan- 

 thion, cannot belong to that genus. 



The larvse which I raised by artificial fecundation from Asteracanthion berylinus 



