56 EMBRYOLOGY OF THE STARFISH. Part I. 



Miiller, the young Starfishes are evidently on the point of resorbing the arms. The 

 larvas present all the appearance of contraction and distortion usually accompanying 

 this process, and Muller's figures agree entirely with the various attitudes which they 

 assume during this resorption. 



If we now turn to his fourth Memoir, which contains the fullest descriptions, we 

 shall see that although in many of the figures of Miiller the Starfish, at least one 

 side of it, has been drawn correctly, yet his statements and some of the figures 

 which he gives, cannot be reconciled with one another. On Plate II. Figs. 5, 6, of 

 his fourth Memoir, we have the evidence, from his own drawings, that his Bipinnaria 

 had two water-tubes ; yet, in the subsequent stages, Miiller says positively that it has 

 only one water-tube, the one with the water-pore, — a statement which is entirely 

 contrary to the earlier stages of his Bipinnaria. From what I have shown of the 

 mode of development of these water-tubes, of their increase in size in proportion to 

 the age of the larva, it is quite improbable, notwithstanding the statement of Miiller, 

 that one of them should disappear ; he also says, that they are not to be 

 confounded with what he calls " wimpernder Schlauch," while our observations of 

 Asteracanthion go to show that these two systems are but one. 



The discovery of the water-pore in Muller's Bipinnaria was a great step towards 

 solving the question of the origin of the madreporic body, which he rightly con- 

 jectures to be nothing but the water-pore. He also notices the rosette of tentacles, 

 or, more properly speaking, the five radiating tubes from which the tentacles eventu- 

 ally branch. He fails, however, to notice that this rosette, like the cap of the Star- 

 fish, as he calls the back, is open; and although he has occasionally represented it as 

 such, he has not perceived the true relation between the positions of these two areas. 

 He says distinctly that the cloak-like envelope, or the abactinal area, originates upon 

 the surface of the stomach, whereas it lies, in reality, upon the surface of the second 

 water-tube, which he says does not exist in his Bipinnaria; while the water-system, 

 or the ambulacral system, originates on the water-tube in such a way that the two 

 open warped pentagonal surfaces make a very large angle with one another; Miiller, 

 however, did not notice that they were open and warped surfaces. 



Van Beneden's observations, in which he says that the two branches of the Y- 

 shaped water-tubes are separate in the young, and become united in the adult, are 

 fully confirmed by my observations. Miiller has called these small bodies, while 

 they are still separate, problematic bodies ; he says they disappear in older larvas, 

 and have nothing to do with the " Schlauch-System." It is evident, from my obser- 

 vations, that the Schlauch-System is only the advanced condition of the problematic 

 bodies, which are isolated on each side of the body in the young larvae (see Pis. 

 II., HI. of this Memoir, and Van Beneden's Brachina), and become united in a Y- 

 shaped water-system (Schlauch-System), when they reach the condition of Bipinnaria of 



