SHALLOW- WATER STARFISHES 315 



by Mr. Sladen there is a perfectly well defined dorsal or " anal " pore, 

 and in some of the genera the pore is even elevated on the summit 

 of a dorsal cone or chimney (Psilaster, Ily aster, etc.). This pore, 

 which I have designated as " pseudanus" or " nephridial pore" 

 serves in each of these families (and in Asterioidea generally) mainly 

 for the discharge of the secretion of the branched, dorsal, glandular 

 organs, probably nephridial in function, situated above the stomach 

 and often called " cereal appendages." These glands are sometimes 

 absent. Whether the central pore serves as a true anus in any of 

 these starfishes is very doubtful, for the intestine is usually nearly 

 or quite abortive. In any case, it is often impossible to ascertain 

 this point without actual dissection of alcoholic or fresh specimens, 

 which are often not available. 



I have been unable to demonstrate a functional intestine in any 

 case, and have never observed foecal matter in the so-called intestine ; 

 nor have I ever seen such substances discharged by the dorsal pore 

 by any living starfish, though I have studied thousands of living 

 specimens, including numerous genera and families. In Pterasteridae, 

 however, the intestine is very obvious. 



The existence of definite fascicles of specialized spinules or 

 papillae on the margins of the plates, so as to form covered chan- 

 nels along their sutures, in this and the related families, is evidently 

 a character both of morphological and of physiological importance. 

 The existence of such fascicles is correlated with the mode of life. 

 Such forms as have them appear commonly to live more" or less 

 buried in soft mud or sand, and the fascicles are evidently for the 

 purpose of providing a free circulation of water around the whole 

 surface of the body, both to provide for respiration and to keep the 

 surface of the body free from dirt. The paxilliform plates and 

 spinules also contribute to both these functions and also serve to pro- 

 tect the dermis and papulae from dirt. 



The typical Astropectinidae are among those best provided with 

 fascicles and with the most highly developed forms of paxillse. They 

 are also those that are eminently dwellers on and beneath mud and 

 sand. The pointed form of the ambulacral feet is correlated with 

 the same habit, but they are not confined to such places. 



The genera Ctenodiscus, Porcellanaster, Luidia, and allies have 

 similar but even more specialized, structural adaptations for the same 

 purposes. 



Dr. Fisher thinks that it is not possible to divide the family into 

 subfamilies, as others have done. Owing to the recent discovery, in 



