308 'Journal of Cojnparative Neurology and Psychology. 



of Prentiss ^ who, although he is primarily interested in the study of 

 the otocyst, gives some attention to sensory hairs in general. As 

 a result of extended physiological experimentation both he and 

 Beer- deny an auditory function to any setae, whether within the 

 otocyst or without. In other words they assert that the animals 

 give no response to true auditory stimuli, that the otocyst is an 

 organ of equilibration more properly called "statocyst," and 

 therefore that no setae can rightly be called auditory. Prentiss 

 says, "All sensory bristles of decapod Crustacea can be divided 

 into two general types: (i) Tactile bristles, having typically a long, 

 straight, plumed, attenuate shaft, attached at the base by a thin 

 spherical enlargement, which allows great freedom of movement. 

 Auditory hairs, so-called, are merely modifications of these, for 

 all gradations between the two exist. Tactile hairs are found on 

 nearly all the appendages, and on some parts of the body. (2) 

 Olfactory bristles, which are short, cylindrical or slightly tap- 

 ering, and firmly attached as compared with tactile hairs, there 

 being no marked basal enlargement. At the tip the chitin is either 

 pierced by a pore, or ends in a thin, permeable membrane, which 

 allows substances in solution to enter the cavity of the hair. If 

 found on the first or second antennae, they are termed olfactory 

 hairs; when on the oral appendages, taste or gustatory bristles, 

 though their functions are probably the same." Thus the term 

 "chemical hairs" would include both classes, olfactory and gus- 

 tatory, and in view of the practical difficulty of distinguishing 

 between olfactory and gustatory reactions in aquatic animals, 

 would be the better term to apply. It is to be noted that all chem- 

 ical hairs, according to Prentiss, are smooth, or unplumed. In 

 regard to the innervation, all the tactile hairs examined (otocyst 

 and mouth parts) showed the same form, a single nerve fiber 

 running to the base of the hair and terminating in the spherical 

 enlargement without branching, and in no case entering the lumen 

 of the hair proper. The chemical hairs, on the other hand, present 

 quite a different appearance. Here the number of ganglion cells 

 and peripheral fibers going to each hair varied from ten on the 



'Prentiss, C. W. The Otocyst of Decapod Crustacea. Bulletin of the Museum of Comparative 

 Zoology at Harvard College, Vol. 36, pp. 165-251. 1901. 



^Beer, T. Vergleichend-physiologische Studien zur Statocysten function. I. Ueber den angeb- 

 lihen Gehorsinn und das angebliche Gehororgan der Crustaceen. Archiv fiir die gesammte Physiologie, 

 Vol. 73, pp. 1-49. 1898. II. Versuche an Crustaceen. Ihid., Vol. 74, pp. 364-382. 1899. 



