ECHINODERMATA 435 



bulacral surface secretions of calcareous salts, which at first 

 formed delicate rods and subsequently united into reticular 

 plates. Eleven such plates can soon be recognized, a central 

 one and (arranged about it in a circle) two rows of alter- 

 nating plates, the fundaments of the radial and interradial 

 plates. One of the former, which at first lies at the left next 

 to the dorsal pore, subsequently grows around it, and thus 

 becomes the madreporic plate (Ludwig). According to 

 LuDwiG, the ambulacral or vertebral plates of the arms 

 make their appearance very early as five pairs of calcareous 

 bodies at the base of the five hydroccele pockets. They 

 therefore have even now the position which they retain 

 afterwards, namely, on the outer side of the future am- 

 bulacral vessel. The other skeletal pieces of the arm are 

 not developed until later. 



The question now is. What relation does the larval intes- 

 tine have to the newly formed starfish ? The older state- 

 ments are not precise on this point ; for this reason we 

 adhere to the recent investigations of Ludwig on Asterina 

 gibbosa, a form, however, which is developed neither from a 

 Bipinnaria nor from a Brachiolaria (comp. supra, p. 421). 

 Yet in this species the two surfaces of the starfish are 

 established independently, and afterwards unite as described 

 above. From this, one may perhaps conclude that the 

 processes in question resemble those in the typical larvd. 

 In Asterina the stomodaeum of the larva separates from the 

 stomach and hangs down from the larval mouth as an 

 internal blind rudiment. For a time the intestine is without 

 any connection with the outside world. The permanent 

 mouth of the starfish is then developed by an outfolding of 

 the stomach, growing out toward the body-wall and finally 

 breaking through to the outside world. The stomach itself 

 is transmitted to the starfish. It subsequently acquires 

 five outpocketings, which bifurcate at their tips, the funda- 

 ments of the five pairs of intestinal caeca. The larval anus 

 is obliterated even before the union of the intestine with the 

 mouth takes place, and the new anus does not arise until 

 after the formation of the mouth-opening. It breaks 

 through at the margin of the central plate, between it and 



