PARKER. — THE SENSORY REACTIONS OF AMPHIOXUS. 437 



In testing amphioxus for chemical responses I used solutions of 

 sour, sweet, bitter, and alkaline substances, as well as solutions of 

 certain oils and other materials. All these solutions were made up 

 in sea water, and, where the strength is expressed as parts of a molec- 

 ular solution, sea water was used as a basis for this mixture instead 

 of distilled water. 



For a sour substance I used nitric acid. If a pipette full of sea water 

 is discharged gently on the side of a resting amphioxus, there is usually 

 no reaction. On animals thus previously tested a few drops of a 

 ^ solution of nitric acid were discharged successively on the an- 

 terior end, on the middle, and on the posterior end. In all these trials 

 vigorous locomotion was induced ; backward when the region of appli- 

 cation was the anterior end or the middle, and forward when it was 

 the posterior end. When a ^^f^^ solution was applied to the anterior 

 end or to the tail, the characteristic reactions were obtained, but there 

 was usually no reaction when this solution was applied to the middle 

 of the animal. A -^ solution called forth no reaction when applied 

 to the middle or the tail, but only when applied to the anterior end. 

 A ifyg- solution called forth no reactions at all. Hence to solutions 

 of nitric acid the anterior end is most sensitive, the tail next, and the 

 middle least. 



A more detailed study of the anterior end showed the following 

 conditions. In an animal that in its normal state responded when 

 this end was stimulated by a -^'^^ solution of nitric acid, the re- 

 moval of the rostrum and the olfactory pit made no observable differ- 

 ence in its responses, thus confirming Nagel's statement ('94^, p. 192) 

 that the olfactory pit is not essential to the special chemical sensi- 

 tiveness of the anterior end. This pit, which was first described by 

 KoUiker ('43) and was believed by him to be olfactory in function, 

 was found in living animals to be lined with ciliated epithelium, by 

 the movement of which particles of carmine were carried into it firom 

 its poste?-ior edge and discharged from it nnteriorlij. Cutting off also 

 the buccal cirri left the animal still receptive to a ff^ solution. 

 When, however, enough of the anterior end was removed to take away 

 the velar tentacles, what remained could be stimulated only by a 

 ^!^^ or a stronger solution of nitric acid. The high degree of sen- 

 sitiveness of the anterior end is therefore dependent upon parts not 

 farther posterior than the velar tentacles. Since these tentacles and 

 the buccal cirri are abundantly supplied with groups of sense cells 

 (Willey, '94, p. 20), it is not impossible that the great sensitiveness 

 of the anterior end is due to these groups of cells ; but to this question 

 I can give no conclusive answer. 



