PHYSIOLOGY OF SYNAPTULA HYDRIFORMIS 349 



'Tastpapillen.' "Die Lage dieser Papillen macht es wohl ziem- 

 lich unmoglich in ihnen etwas anders als Tastorgane zu vermuth- 

 en." Semper also tried to show that the calcareous bodies in 

 the dermis of synaptids, especially the anchors, serve as 'touch- 

 organs.' He even compared them to the 'Tasthaare' of the cat. 

 Unfortunately for his idea, he was forced to confess "Bei den 

 Synaptiden . . . . ist es mir nie gelungen Nerven bis an 

 die Anker heran verfolgen zu konnen." Semon ('87) found, as 

 did Quatrefages ('42), that Synapta inhaerens could be somewhat 

 roughly rubbed on the skin without eliciting any response from 

 the animal. Since, in addition, chloral hydrate applied to the 

 skin caused a contraction and moving away of the part stimu- 

 lated, he suggested that the 'touch-papillae' were not entirely 

 composed of touch cells, but contained also gustatory cells. 

 Moreover, since pigment was to be found in these 'touch-papil- 

 lae,' he thought that some of the cells might serve to receive pho- 

 tic stimuli. Practically all other investigators, however, have 

 been content to ascribe simply a tactile function to these organs. 



b. Observational. The order of diminishing sensitivity to 

 touch in the different body regions of many of the lower animals 

 is anterior, posterior, middle (Parker, '08; Crozier, '14 a). This 

 order holds for Synaptula hydriformis, where the sequence is 

 tentacles, anterior part of the body, posterior part, middle. 

 Table 2 gives a series of reactions obtained by touching the dif- 

 ferent parts of the body with the blunt end of a needle when the 

 animal was moving back and forth just beneath the surface of 

 the sea-water in a finger-bowl. Similar reactions, though much 

 more variable, were given if the animal was stimulated while 

 moving along the bottom of the dish. In most cases a less vig- 

 orous stimulus was required to cause complete withdrawal of the 

 tentacles when the Synaptula was at the bottom than when it 

 was near the top of the water. 



Of these reactions the only one which can clearly be called 

 positive is the response of the outer surface on the tentacle to a 

 very slight touch. This positive thigmotropism is probably the 

 chief cause of the constant motion of the tentacles. The free 

 tentacles are continully attempting to attach themselves, and 



