BIPIXNARIA A8TEKIGERA. GO 



the back, is open ; and althougli he lias 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 witer-tube, which he says does 

 not exist in his Bipinnaria ; while the water-sj'stein, or the ainbulacral 

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

 warped pentagonal surfaces, the actinal and the abactinal areas, 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 fidly confirmed by my observations. Miiller has called 

 these small bodies, while they are still separate, problematic bodies ; he 

 says they disappear in older larvae, and have nothing to do with the 

 " Schlauch-System." It is evident, from my observations, 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 larva? (see Pis. II., 

 III. of this Memoir, and Van Beneden's Brachina), and become united 

 in a Y-shaped water-system (Schlauch-System), when they reach the con- 

 dition of Bipinnaria of Miiller. It would seem, from his figures, as if 

 the abactinal pentagon closed, while the Bipinnaria is still visible. I am 

 rather inclined to think that more advanced larvte will be found to be 

 Brachiolaria-like, as is the case with our Starfish and the Brachiolaria 

 from Messina ; and that this apparent closing up is due to the fact that 

 the larva is not in its normal state, or that the drawings are made some- 

 what foreshortened. In the second Memoir of Miiller, on Plate I., we 

 see that the Y-shaped water-system (Schlauch-System) has been noticed 

 in tw^o of the larvae (Figs. 4, 7), while in the intermediate stages, and 

 in younger larvse, it has escaped his notice. It is undoubtedly to Miiller's 

 want of acquaintance with the earlier and later stages of his Bipinnaria 

 that we must ascribe the discrepancies in his observations. Many of the 

 more important points in the structure of the young larva? naturally es- 

 caped Derbes and Krohn, who were not fiimiliar with the adult lawa?; 

 neither of these observers tells us anything of the presence of the water- 

 tubes, or of the first appearance of the young Echinoderm. 



Bipinnaria asterigera. — Miiller's views concerning the ditlerent organs of 



