80 EMBRYOLOGY OF THE STARFISH. 



Ecliinoderms, 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 Ctenophora?, nor on Balanoglossus, published in the 

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

 at tlie 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 i-apidity 

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

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

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

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

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

 Avater-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 oidy afterwards, when the pentagon of tentacles is formed. 

 The mouth is placed wnthin 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 tlie Starfish. 



The Brachiolarian and Plutean stages are the Acalephian stages of the 

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

 their Polyp stage ; Avhile the arms of the Pluteus stage, Avith their cords 

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

 tions of the spheroinere, covered with locomotive flappers as in Euramphnea, 

 and other Ctenophora?. The resemblance of the larva^ of Echinoderms to 

 Ctenophorce had already been pointed out by Baer, and more recently 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. Leuckart, in his Bericht for 1862, simply says that 

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

 homology holds good. A writer in the Natural History Review for 1861 



