334 J. M. D. OLMSTED 



many quite transparent individuals of a very pale flesh color 

 which appear light green when placed on green sea-weed, and 

 a light red on red sea-weed. Clark ('07) reports that he found 

 synaptulas more abundant on green Ulvaceae, but I collected 

 comparatively few specimens from green sea-weed, obtaining 

 them almost exclusively from red algae growing in shallow water 

 on broad sheltered flats (Millbrook Creek) . There was absolutely 

 no 'outspoken mimicry' of the environment by the animal such 

 as Semon ('87, p. 280) describes for several species, since both 

 red and green synaptulas occur on both red sea-weeds and green 

 ones. Dr. W. J. Crozier informs me that he has found this 

 species in August on the outer reefs in the brown Sargassum, and 

 that the red and green varieties were present there in equal 

 numbers. In my collecting, by far . the greater number were 

 taken at the base of clumps of red sea-weed, where a slate color 

 or even black prevailed (Clark, '98, p. 56). 



The work was done at the Bermuda Biological Station for 

 Research during the summer of 1916. I wish to thank the trus- 

 tees of the Humboldt Fund and Dr. E. L. Mark for making it 

 possible for me to go to Bermuda, and also Dr. W. J. Crozier 

 for suggesting this species to work upon. Further acknowledg- 

 ment is due Dr. Mark for his helpful criticism of the manuscript. 



I. GENERAL PHYSIOLOGY 



1. Locomotion 



Locomotion through sea-weed is accomplished largely by 

 means of the tentacles, though movements of the body in the 

 form of peristaltic waves assist. That the tentacles subserve 

 locomotion, as well as the sense of touch, in holothurians was 

 first shown by Tiedemann (1816). The locomotor function is 

 so emphasized in this particular species that Lesueur ('24) in his 

 original description of the species says : "In locomotion the ten- 

 tacles are used as feet." It is interesting to note that the second 

 time this species is mentioned, this characteristic is again re- 

 ferred to, for " there can be no doubt that Pourtales' ('51) 

 Synapta from Biscayne Bay, which he called viridis, is identical 



