Chap. IV. BIPINNARIA ASTERIGERA. 57 



Midler. 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 

 larvas 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 somewhat fore- 

 shortened. In the second Memoir of Midler, on Plate I., we see that the Y-shaped 

 water-system (Schlauch-System) has been noticed in two of the larvas {Figs. 4, 7), while 

 in the intermediate stages, and in younger larvae, it has escaped his notice. It is 

 undoubtedly to Midler's want of acquaintance with the earlier and later stages of his 

 Bipinnaria, that we must ascribe the discrepancies which occur in his observations. 

 Many of the more important points in the structure of the young larvas ; naturally 

 escaped Derbes and Krohn, who were not familiar with the adult larvas; neither of 

 these observers tell us anything of the presence of the water-tubes, or of the first 

 appearance of the young Echinoderm. 



Bipinnaria asterigera. — Midler's views concerning the different organs of Bipinnaria 

 asterigera of Koren and Danielssen are undoubtedly correct. What they took for a 

 respiratory opening, leading into the cavity, is the mouth ; they had correctly seen 

 the anus, as well as its connection with the intestine of the Starfish. Judging from 

 the figures of Midler, and of Koren and Danielssen, there are evidently striking 

 differences, in the termination of the intestinal canal, from that of our Starfish. In 

 Bipinnaria asterigera the anal opening is on the abactinal side of the Starfish, whde 

 in our young Starfish it is still on the actinal side. The position of the young 

 Starfish, with reference to the stomach of the larva, seems still to require further 

 investigation, as it is not possible to say, from the figures of Miiller, or from those 

 of Koren and Danielssen, what is its true relation, and whether it has the same 

 oblique j^sition which it occupies in our young Starfish. The investigations of 

 younger specimens than those examined by Miiller, or Koren and Danielssen, will 

 at once settle this point, as well as the mode of formation of the mouth of the 

 young Starfish, and its separation from the Bipinnaria. From the figure given by 

 Miiller, in his third Memoir (PL VII. Figs. 5, 6, 7), I am led to think that the 

 position is also an oblique one ; and that, though the Starfish may separate from 

 the Bipinnaria, yet it is undoubtedly the opening of the oesophagus into the stomach, 

 which becomes the future mouth of the Starfish, as in our Asteracanthion. In his 

 third Memoir, Miiller shows conclusively, that the madreporic body is not the scar 

 left by the junction of the young Starfish with the Bipinnaria, but corresponds to 

 an opening leading into a short tube between two of the arms ; and also points 

 out the probability of its correspondence with the opening leading into one of the 

 water-tubes which he had noticed in Auricularia. This supposition is fully con- 

 firmed by the observations we have made of the coincidence of the water-pore 



