l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. ^2 



barnacles. The starfishes are largely carnivorous, feeding especially 

 upon molluscs, but some swallow mud out of which they digest the 

 organic matter. The echinoids feed upon vegetable matter or upon 

 organic detritus, and many are mud or sand swallowers. The 

 ophiurans feed largely upon detritus or swallow mud, but many are 

 ectoparasitic upon coelenterates and crinoids from which they steal 

 the food in or on its way to the stomach. 



Thus along with the widening of the gap between the structure of 

 the true barnacles and that of the echinoderms there is a similar 

 divergence in their feeding habits ; from plankton feeders they become 

 simply scavengers and parasites. 



The recent crustaceans as a whole show exactly the same line of 

 specialization from the phyllopod, which feeds on minute organisms, 

 to the decapod, which feeds largely on carrion or detritus, or is 

 ectoparasitic on coelenterates or on crinoids, and this development of 

 the feeding habit, with the emphasis on the scavenging activities, is 

 characteristic of these two groups alone. 



PROFESSOR PATTEN'S INTERPRETATION OF THE AFFINITIES 

 OF THE ECHINODERMS 



Although I arrived at the conclusion that the echinoderms and the 

 arthropods are in reality closely related more than ten years ago and 

 in a short paper published in April, 1910, that conclusion is readily 

 to be inferred. Professor William Patten was the first to attempt to 

 explain the relationships of the echinoderms to the arthropods in 

 detail. His reasoning is so entirely dififerent from mine that it is 

 worth while to repeat his arguments here. 



He says : " The echinoderms are notable for their contrasts and con- 

 tradictions. Their outward appearance and their pronounced radial 

 structure distinguish them from all other animals, and at first 

 sight suggest a very primitive organization similar to that of the 

 coelenterates. On the other hand they display a high degree of his- 

 tological and anatomical specialization that is in marked contrast with 

 their low grade of organic efficiency. They begin their early em- 

 bryonic development with a bilaterally symmetrical body and with clear 

 indications of metamerism, only to change it in the later stages for one 

 that is radially symmetrical and in which all outward traces of 

 metamerism have disappeared. After a short free-swimming larval 

 existence they attach themselves, neural side down, by means of larval 

 appendages and a cephalic outgrowth ; they then turn neural side up 

 and remain so attached for life; or in some cases they give up their 



