THE TWENTY-RAYED STARFISH. 



213 



bcsi, and A. I'ldgaris) has not been easy to determine in the adult. 

 Although Dr. Cole, as we have seen, comes nearest to establishing 

 an anterior pole in the five-rayed starfish, A. forbcsi (Fig. 8). 

 Jennings Co/), in experiments on righting reactions, also found 

 that : " Individual starfish do have a more or less permanent ' set ' 

 toward the use of a certain ray in pulling themselves over in the 





FIG. 10. Photograph of a small specimen of Pycnopodia helianthoides 

 with 14 rays. Notice five rays on one side, and two on the opposite side, are 

 regenerating from autotomy. Rps, respiratory papilla. Natural size. Photo 

 by author. 



i 



righting reactions." A. forrcri uses the same ray (e.g., ray e, vide 

 Fig. 8) that A. forbcsi uses as anterior pole. This anterior pole 

 seems to be directly homologous with the anterior end in Pycno- 

 podia, judging the size of the rays and their relation to the smaller 

 ones in the latter. 



The number of madreporites, especially in multiradiate species, 

 may vary : Cuenot ('91), Ludwig ('99), Delage et Herouard ('03), 

 Sedgwick ('09), Verrill ('14), Crozier ('21), and on that account 

 the true position of the madreporite is difficult to determine. In 



