PHYSIOLOGY OF SYNAPTULA HYDRIFORMIS 367 



animals. Clark ('98, '07) has followed Semon's example in 

 calling the cups on the tentacles gustatory organs. He re- 

 marks, " There seems to be little doubt that these cups serve 

 as organs of either taste or smell, although the evidence is not 

 conclusive." 



There are, however, synaptids which lack these cups, among 

 them is Synaptula hydriformis, and yet this species is very sen- 

 sitive to chemical agents. The function of the 'gustatory cups' 

 therefore seems to be still unsettled. Clark ('07) states that 

 synaptids which possess eye-spots never have gustatory cups, 

 and vice versa. Upon the ground that the functions of these 

 two organs are those suggested by their names, the relation of 

 the presence of one of these organs to the absence of the other 

 is hard to explain. 



b. Observational. Synaptula hydriformis, like the majority 

 of aquatic animals, is sensitive to chemical agents over the 

 entire body. The most vigorous reactions are given when the 

 tentacles or the head end are stimulated. For this reason ex- 

 periments to determine the limits of sensitivity were per- 

 formed by allowing 0.5 cm. of a solution of a given reagent 

 to flow down the inside of the vessel for 2 to 3 mm. till it 

 reached the surface of the water directly above the tentacles 

 of an animal moving about just under the surface. More 

 constant reactions were obtained when the animal was tested in 

 this position than when it was crawling on the bottom of the 

 dish. Trials with ordinary sea-water were made before each 

 experiment, and often between successive exposures to the 

 chemical solution. With rare exceptions there was no response 

 to sea-water. Ten minutes was allowed between successive trials, 

 so that fatigue of the sense organs might not occur, and so that 

 the animal might resume its position at the top of the dish if it 

 had dropped to the bottom. In general the same chemical 

 agent was not used in two consecutive trials in order to avoid 

 a possible accumulative effect. The following record is typical, 

 x denoting no response. 



