42 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



as a whole homologous with the longitudinal muscles of the echinoids (Echinothuridae) 

 and holothurians. Since the ligaments of the syzygies are identical in structure 

 with those of the dorsal ligament bundles of the muscular articulations, the breaking 

 apart of the syzygies is assumed to result automatically from any stimulus, such as 

 panic, which causes the ventral muscles to become inert and the dorsal ligament 

 fibers to contract to the fullest extent, this contraction being accompanied by a 

 much less contraction of the syzygial fibers which, being very short and normally 

 under more or less tension, are torn across. In adolescent autotomy the syzygies 

 are assumed to be broken across by growth changes. 



A new comatulid from the Solomon Islands, Colobometra diadema, was described 

 on March 23. 



In one paper published in April the similarity of the nervous system of the 

 crinoids to that of the arthropods was discussed, and in another the pentamerous 

 symmetry of the crinoids was considered. It was pointed out that in the case of 

 4-rayed comatulids it is always the anterior ray that is missing, and that therefore 

 5-rayed examples are the equivalent of 4-rayed individuals plus the addition of half 

 of a pair of appendages between the two of the anterior pair. It is suggested that 

 the 5-rayed condition may have arisen in this way from a 4-rayed bilaterally sym- 

 metrical ancestor, and a step in this direction is seen in the case of those 5-winged 

 insects (a 5-winged specimen of Platysamia cecropia is figured) in which the additional 

 wing is inserted in advance of one of the wings of the anterior pair. It is stated 

 that larval echinoderms are as extraordinarily specialized as the adults, but along 

 radically different lines, and therefore they must be treated almost as a different 

 class of animals from the adults, specialized along entirely different lines and fitted 

 for an entirely different mode of life. 



In a third paper published in April attention was called to the striking similarity 

 between the side- and covering-plates of the crinoids and the scutes developed in 

 winter along the sides of the toes in the ruffed grouse (Bonasa umbellata) to increase 

 the area of the foot. It is suggested that the adambulacral plates in the crinoids 

 serve in the same way to increase the area upon which minute animals in falling 

 would be conducted to the mouth, and further that the prevalence of these plates 

 in the crinoids of deep water and their almost entire absence in the crinoids of the 

 littoral may be due to the fact that, while the former depend chiefly for their food 

 upon dead animals falling from above, the latter subsist upon living microplankton, 

 which naturally would recoil from contact with these plates. 



The phylogenetic interrelationships of the recent crinoids (considered entirely 

 apart from the fossil species) were considered in a paper published on May 3. The 

 characters used are almost entirely those found in the column. The groups in 

 phylogenetic sequence are : 



Holopodida: 

 Holopus. 



Ptilocrinida : 



First group 



Rhizocrinidae (Rhizocrinus; Bathycrinus) . 

 Phrynocrinidae (Phrynocrinus). 



