PHYSIOLOGY OF SYNAPTULA HYDRIFORMIS 365 



Water at 27° was first run through. It was found that there 

 was no response when the tube was held near a Synaptula, or 

 even when it touched the animal, if this was done with sufficient 

 care, except that when in contact with the tentacles they would 

 attach themselves to the tube and the animal would attempt to 

 climb along the tube. Water at 47° and even at 50° failed to 

 show any effect, although both temperatures are above the 

 killing point, and the water surrounding the U-tube must have 

 been raised considerably above 27°. Indeed, the action of the 

 tentacles was the same as when the water at 27° was running 

 through it, since they attached to the tube in the same manner. 



From these results one must conclude that the temperature 

 sense of Synaptula hydriformis, while not entirely absent, is very 

 poorly developed and probably not located in any particular 

 regions. Since in its natural habitat the animal is not sub- 

 jected to sudden or great changes of temperature, it is not 

 surprising to find this sense practically lacking. 



5. The effect of chemical agents 



a. Historical. Chemical agents may produce in vertebrates 

 the sensation of smell or taste according as they stimulate the 

 olfactory or gustatory organs, or they may affect the free nerve 

 endings of the epidermis, the receptors for the common chemical 

 sense (Parker, '12; Crozier, '16 a). These three kinds of re- 

 ceptors are found in aquatic as well as land vertebrates (Sheldon 

 '09; Parker, '12). Among aquatic invertebrates some mollusks 

 have been shown to have separate senses of smell and taste 

 (Kafka, '14, p. 269), as proven by topographical experiments 

 and by the difference in histological makeup of the organs. 

 Copeland's ('17) recent experiments on snails give further 

 proof of the separateness of these senses in mollusks. 



Among the echinoderms the starfish was thought by Romanes 

 ('85) to have a sense of smell located in the ventral surface 

 of the rays. More careful experiments by Jennings ('07) on the 

 starfish Asterias forreri showed that the pedicellariae on the 

 dorsal surface responded to the juice of crab-meat held a little 

 above the surface of the animal. It is therefore probable that 



