80 EMBRYOLOGY OF THE STAEFISH. 



Echinoderms, but also with several errors contained neither in the ab- 

 stract nor in the original. He does not appear to know my paper on 

 the Embryology of Ctenophorae, nor on Balanoglossus, published in the 

 Memoirs of the American Academy in 1873 and 1874, and distributed 

 at the time ; consequently, in what he now writes, the older views re- 

 garding the affinities of Echinoderms with Coelenterata and Annelids, which 

 had been discussed from a different standpoint, do not receive the least 

 recognition. 



The mode of development of these two types having been shown to be 

 on one and the same pattern, modified in such a way that a like re- 

 sult is reached either by fewer stages or by a greater or less rapidity 

 in the process, it remains for me to show that the larva? we have had 

 before us, in the complicated form of a Brachiolaria or a Pluteus, is really 

 built upon the radiate plan. We find a good starting-point in the water- 

 tubes, which, as I have shown, become the circular tube of the 3'oung 

 Starfish, from which the ambulacral system is afterwards developed. This 

 water-tube, it is true, is not circular; it is not continuous, and yet it is 

 the homologue of the circular tube of Acalephs, the radiating tubes being 

 developed only afterwards, when the pentagon of tentacles is formed. 

 The mouth is placed within this circular tube ; and the fact that the 

 mouth of the larva is brought, by the contraction of the oesophagus, close 

 upon the stomach, does not change its position with reference to this 

 circular tube. The water-system contracts with it, changes its position, 

 and surrounds eventually the new opening, by the flattening and closing 

 of the Starfish. 



The Brachiolarian and Plutean stages are the Acalephian stages of the 

 Kcliinoderms, corresponding to the Hydrarium forms of the Acalephs, in 

 their Polyp stage ; while the arms of the Pluteus stage, with their cords 

 of locomotive cilia, recall strongly the strange filiform appendages of por- 

 tions of the spheromere, covered with locomotive flappers as in Euramphaja, 

 and other Ctenophoras. The resemblance of the larvre of Echinoderms to 

 Ctenophora^ liad already been pointed out by Baer, and more recenlh' by 

 Professor Agassiz, who was not then acquainted with the observations of 

 Baer, This comparison seems to have found but little favor with more 

 recent investigators. Lcuckart, in iiis Bericht for 1862, simply says that 

 no furtiicr proof has been adduced by Professor Agassiz to show that the 

 homology holds good. A writer in the Natural History Review for 1801 



