BCHINODERMATA 



438 



The earliest trace of the starfish is formed in the posterior 

 part of the larval body. The five-rayed f andament of the 

 water- vascular system lies at the left of the stomach (Fig. 

 209 -ff), while on the right side of it an accumulation of 

 mesenchyma cells takes place, in which the first skeletal 

 parts are already secreted (Fig. 209 K). The ventral or 

 ambulacral side of the starfish is indicated by the water- 

 vascular rosette, and the dorsal or antambulacral side bv 



B-y 



Fig. 209. 



Fig. 210. 



Figs. 209 and 210. — Bipinnaria larvae with the fiindament of the starfish in 

 different stages of development (after Joh. Mullke). A, anus ; D, intestine ; H, 

 water-vascular rosette ; K, calcareous secretions lying in the fundament of the 

 antambulacral surface of the starfish j M, mouth ; p/, preoral area of the larva ; 

 W, ciliated band. 



the skeletal structures. The two sides are established inde- 

 pendently. Even at a very early period the five-rayed 

 structure of the starfish can be recogrnized in them. This 

 is indicated on the ambulacral surface by the fact that five 

 folds arise in the larval skin immediately over the radii of 

 the water-vascular rosette, while on the antambulacral sur- 

 face the calcareous rods are deposited in the form of a 

 pentagon. On both sides a thickening of the epidermis is 

 connected with the diffei'entiation of the cutis-forming 



K. H. E. 



F F 



