242 W. J. Crozier, 



logical anterior of spataiigoids , and the interesting possibility 

 suggests itself that the intensity of physiological polarization ^) in 

 echinoderms is correlated with the degree of morphological diffe- 

 rentiation about a longitudinal axis. With the holothurians, in 

 which this sort of anatomical arrangement is most obvious, homo- 

 logies are made difficult by reason of the assumption, in these forms, 

 of a horizontal axis morphologically perpendicular to that of the 

 Asteroids and Echinoids. Thyone hriareiis, the only pedate species 

 which has thus far been studied, apparently moves with sjoj part 

 of the body to the front (Peaese, 1908, p. 278). Holothuria, however, 

 affords considerable support to Cole's idea, for the three species 

 of this genus which I have studied were never observed to crawl 

 in any other way than with the anterior end in advance, and the 

 same statement applies to Stichopus. The locomotion of H. surina- 

 mensis was carefully studied with respect to this point. Backward 

 crawling could not be secured by seemingly appropriate stimulation 

 experiments; the direction of H. surinamensis' progression is as de- 

 finitely fixed as is that of gasteropod mollusks (cf. Parkee, 1911). 

 To test the possibility of reversed crawling, a number of animals 

 were placed in horizontal glass tubes of such a diameter as to 

 allow only a little space between the wall of the tube and the 

 animal's body. Irrespective of the direction of the incident light, 

 movement was always in a forward direction. In tubes with one 

 end sealed, holothurians would remain with the tentacles closely 

 pressed against the sealed end until death ensued (in 12 — 24 hours) 

 through the absence of adequate oxidation and the toxic action of 

 excretory products. A few individuals managed to escape from 

 tubes having one end closed, but this was accomplished by so 

 twisting the body as to bring the anterior end toward the opening 

 of the tube. It is probably in this manner that the holothurians 

 adjust themselves in narrow holes in rocks with the tentacular end 

 outward. Burrowing is accomplished, as in Synapta (Claek, 1901a), 

 Caudina (Geeould, 1896), and other holothurians (Sempee, 1868), in 

 a slanting direction, with the anterior end directed downward. 

 Animals from which the anterior end, including the nerve ring and 

 associated structures, had been removed by a transverse cut, like- 

 wise consistently moved with the anterior end to the front, as, for 

 example, in the following experiment: 



1) The term polarization here means merely antero- posterior 

 differentiation. 



