42 EMBEYOLOGY OF THE STAEFISH. 



contraction of the anal tentacles, nothing is to be seen of the larval ap- 

 pendages, except a few indistinct swellings on the actinal side of the little 

 Starfish (PI. VI. Fig. 1). 



The Starfish after the Eesorption of the Bipimntria. — The process of resorp- 

 tion, which I have frequently had the opportunity to examine and trace 

 in all its stages, leaves no doubt, at least in this case, that the young 

 Starfish does not separate from the Bi-achiolaria. We cannot, therefore, 

 consider the Starfish and the framework (the Brachiolaria) as two indi- 

 viduals, leading a separate existence at different stages of growth, but 

 must regard them both as one and the same thing. This is in direct 

 contradiction to the statements of Mliller, and of Koren and Danielssen, 

 with regard to the Echinoderm, the development of which they have had 

 occasion to watch. I must add that my own observations concerning the 

 development of Echinoids and of Ophiurans have led nie to an entirely 

 different opinion from the one they have expressed ; see my remarks on 

 the Embryology of Echinoderms, in the Memoirs of the American Academy 

 for 1864. 



Closing of the Actinal and Abactinal Areas. — Although the young Starfish 

 has noAv resorbed all the appendages of the Brachiolaria (PI. VI. Figs. 

 1, 2, 3, 4, 6, 7), it is very different from the adult; the rays do not yet 

 make a comjjlete circuit, nor are they similar to each other; the penta- 

 gon of tentacles is still open, and the first step, preceding any other great 

 change, is the closing of the actinal and abactinal areas, by which the 

 two regions are brought into their proper relations. While the arms of 

 the larva are shrinking aAvay, the tentacular and abactinal pentagons are 

 drawn closer together by the contraction of the water-tube. The ex- 

 tremities of the two open pentagons approach each other simultaneously 

 by the flattening, in opposite directions, of the two pentagonal spirals, 

 until the surfaces are brought into parallel planes, and the space, still 

 separating the two ends of the pentagon (PI. VI. Fig. 4) gradually dimin- 

 ishes, when they finally join ; the Starfish is then in its normal con- 

 dition, and the circuit is completed, though the embryo is by no means 

 synniietrical. 



[Metschnikoff' has since also shown the same thing in his development 

 of an Ophiuran. See 1. c. PI. IV.] 



Development of the Avihilacral Tentacles of the Starfish. — While the closing 

 of the spiral goes on, the pentagon of the tentacular side is undergoing 



