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 Brachiolaria. 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 still take place to produce the Echinoderm proper. However wonder- 

 ful the process by which an animal seems to pass from a radiate form, to an 

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

 which this seeming bilateral animal is again reduced to a strictly radiate structure, 

 are perhaps still more remarkable. 



For the development of the Starfish itself, we must turn back and examine 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 disappeared, and has been 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 Muller and of Koren and Danielssen respecting Bipinnaria asterigera ; 

 where it is said that the Starfish and the Bipinnaria separate, both becoming free. 

 The process by which the young Starfish eventually resorbs the Brachiolaria (PL 

 IV". Figs. 7, 8, 9) is similar to that observed by Sars* in the development of Echi- 

 naster, where the whole larva and all its appendages are gradually drawn into the 

 body, and appropriated during the growth of the young Starfish. 



It has already been shown that the anal portions of the water-system, as they 

 increase in size, spread little by little over the surface of the stomach ; the edges 

 creeping towards each other and surrounding the stomach on both sides, like a 

 cap, yet without uniting. The funnel leading from the dorsal pore shortens, as 

 the water-system extends towards the dorsal region, and the anal extremities of 

 the water-tubes come so near together (PL V. Figs. 1, 2, 3, 5, w, w) that we might 



vol. v. 4 (25) 



