312 Dr. O. vom llatli on the 



The ncvvc-cnd apparatus is so similar in structure in tiie 

 different sense-organs that, as it seems to me, it cannot bs 

 made use of for this purpose ; we have therefore to consider 

 in the first place the form and mode of attachment of the 

 hairs, as well as their number and position. Those capilli- 

 form structures wliich do not terminate in a sharp point, an I 

 which at their distal, usually paler, and thin-walled end, as is 

 shown by the experiments detailed above, permit the entrance 

 of chemical substances dissolved in water, will at once, with 

 some degree of probability, be explained as olfactory or 

 gustatory organs. Those plumose hairs which rest upon an 

 unusually delicate domed membrane, and which are therefore 

 very easily set swinging, are regarded as auditory organs. 

 Those sensory hairs wdiich in all probability serve neither 

 the olfactory nor auditory function are designated tactile 

 setae. In drawing these distinctions it is by no means main- 

 tained that the functions specified are so sharply delimited 

 from one another, and that possibly the same hair may not 

 serve in several of the above-mentioned capacities at once. 

 Let us now enquire how the various organs are distributed 

 upon the body. 



The olfactory organs (olfactory tubes) are situated exclu- 

 sively upon the first antenuEe in all the Crustacea which we 

 have examined, with the exception of Nchalia and Duistylis^ 

 in wdiich they occur upon the second antennaj also. In my 

 opinion these organs probably serve in the first place to scent 

 out food and tlie opposite sex ; in the case of the aquatic 

 forms they would have the general function of testing the 

 chemical conditions of the water. In exclusively terrestrial 

 Crustacea, <?. ^. the Woodlice, they would in all probability 

 enable the animal to find out the constitution of the atmo- 

 sphere, and in this sense might be designated olfactory organs. 

 In discussing the olfactory tubes we must also allude to the 

 fact that they are more powerfully developed in the blind 

 Crustacea than in their nearest allies possessing eyes ; and 

 the interesting circumstance that these organs are usually 

 more numerous and larger in the sexually mature male than 

 in the female is also worthy of notice. The theory has often 

 been advanced by authors that the females at the period of 

 maturity of the ova emit a glandular secretion, wliich is 

 detected by the niale by means of his olfactory organs. In 

 the case of the freshwater Copepods, Vosseler * states it as a 

 fact that " the females are discovered and fertilized by the 

 males at night, and even by day, the male must possess other 



* Julius Vosselor, ' Die freilebenden Copepodou ^^'lirtU'Iubt.■r^'s,' Dis- 

 sertiitiou. Stuttgart, 18S(}. 



