PHYSIOLOGY OF SYNAPTULA HYDRIFORMIS 347 



4. Other muscular activities 



a. Blood vessels. Microscopic examination failed to show any 

 movement in the walls of the dorsal and ventral blood vessels. 

 As Clark ('07, p. 63) states, the blood is moved by the contrac- 

 tions of the muscles in the wall of the alimentary canal. One 

 can see the cells which lie in the lumen of the blood vessel shift 

 back and forth as a peristaltic wave passes down the intestine. 



b. The gonads. The gonads, however, as Clark ('98, p. 58) 

 also observed, possess the power of independent movement. 

 These movements consist of irregular twitchings, and last for 

 some 30 minutes after removal from the body. Histological 

 study has shown the presence of muscle fibers in these 'genital 

 tubes' (Clark, '07, p. 59). 



5. Bacterial parasites 



Clark ('98, p. 56) found 'no internal parasites' in the synaptu- 

 las which he collected at Jamaica. In nearly every one taken 

 at Bermuda there were one to four dark brown or green, almost 

 black, spherical masses, ranging in size from mere specks to 1.5 

 mm. in diameter. These spheres always lay free in the body- 

 cavity and shifted back and forth with the movements of the 

 animal. When these bodies were crushed and examined under 

 the microscope, they were found to consist of bacteria belonging 

 to the genus Microcystus. 



Experiments on sensory reaction of this Synaptula were con- 

 ducted on both red and green varieties, but upon comparing 

 records of the animals of the two colors, no difference whatso- 

 ever could be found between the behavior. 



Summary of Part I 



1. There is no mimicry of its environment by Synaptula 

 hydriformis. 



2. Attachment of the tentacles is probably by an adhesive 

 secretion alone, not by suction. 



