CHAPTER SECOND. 



HISTORY OF THE DEVELOPMENT OF THE STARFISH PROPER. 



We have thus far described the changes the embryo undergoes from 

 the time it leaves the egg, and have traced its gradual transformation 

 into the complicated being called Brachiolai'ia. All the phases through 

 which the embryo passes thus far have not the least resemblance to a 

 Starfish, nor have we yet alluded to any of the changes which must take 

 place to produce the Echinoderm proper. However wonderful the process 

 by which an animal seems to pass from a radiate form to an apparently 

 bilateral one be, the changes we shall now see taking place, by which 

 this seeming bilateral animal is again reduced to a strictly radiate struc- 

 ture, are perhaps still more remarkable. 



For the development of the Starfish itself, we must turn back and ex- 

 amine the larva in some of its younger stages, in order to trace the first 

 changes in its anal extremity. There alone transformations take place 

 affecting the development of the Echinoderm proper, until the whole of 

 the complicated framework upon which the Starfish is fastened has dis- 

 appeared, being resorbed by the very Echinoderm it has helped to 

 raise. The Brachiolaria is completely drawn into the body of the young 

 Starfish, before it leads an independent existence. This is contrary 

 to the observations of Miiller and of Koren and Danielssen respecting 

 Bipinnaria asterigera; where it is said that the Starfish and the Bipin- 

 naria separate, both becoming free. [Metschnikoff's and my own observa- 

 tions on this point seem to throw doubt on the separation of the Pluteus 

 and of the Echinoderm, so that renewed observations are necessary regard- 

 ing the Bipinnaria of Koren and Danielssen to establish the fact which thus 

 far is contrary to all the observations of Miiller, MetschnikofF, and myself 

 on the Starfish Pluteus, and on the other orders of Echinoderms.] The 

 process by which the young Starfish eventually resorbs the Brachiolaria 

 (PI. IV. Figs. 7, 8, 9) is similar to that observed by Sars in the develop- 



