Chap.V. plan of development of ECHINODERMS. 63 



Echinaster type ; in either of the orders, it is one and the same thing differently car- 

 ried out. The larva? of our Cribrella, which I have had frequently occasion to 

 examine, have satisfied me that the process of development is the same, with the 

 exception that it is shorter. The larvse of Ophiurans, which Professor Agassiz has 

 examined at Charleston, would lead to the same conclusion with reference to the 

 Ophiurans ; while, from the drawings of Miiller, it is easy to satisfy one's self, with the 

 above data, that the two types of development of Holothurians, examined by him, 

 are only modifications of each other. As the only larvse of Holothurians, which I 

 have seen, belong to the " Wurmfdrmiger " type, I am unable to state this from 

 actual observation. It is evident that we have also in Comatula these two types of 

 development. Professor Agassiz has frequently observed in a species of Comatula 

 found in Charleston, S. C, that the young embryos remain attached to the parents ; 

 while Thompson and Busch have found the larvae swimming freely about. 



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

 the same pattern, modified in such a way that the same result 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 Brachio- 

 laria 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 

 young 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 homo- 

 logue of the circular tube of Acalephs, the radiating tubes being developed only after- 

 wards, 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 refer- 

 ence 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 Echino- 

 derms, corresponding to the Hydrarium forms of the Acalephs, in their Polyp stage ; 

 the arms of the Pluteus stage, with their chords of locomotive cilia, recalling 

 strongly the strange filiform appendages of portions of the spheromere, covered with 

 locomotive flappers, as in Euramphaea, and other Ctenophoraa. The resemblance of 

 the larva? of Echinoderms to Ctenophorae 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 investigations. 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 seems to consider 



