Dermal Sense- Organs of the Crustacea. 305 



importance tlian those of the first *. Typical olfactory tubes 

 have been discovered upon the second antennae, which are 

 also designated tactile antennae, only in Nehalia and Diasfi/lis, 

 through the researches of Claus. 



Tactile hairs, liowever, occur in abundance upon the second 

 antenna?, and may exhibit great differences in number, size, 

 and shape, while here and there they constitute forms which 

 are transitional to the olfactory tubes. To this category also 

 belong the cylinders or clubs of the lower antennae of Gam- 

 marvs puteanus (Leydig). Whether the plugs which are 

 found at the tip of the large (second) antenna of the woodlice 

 have the value of a more highly differentiated sense-organ, 

 or whether they likewise are tactile in function, has not been 

 decided. It is also not unusual to find upon the second 

 antennae feathered hairs which are easily movable and stand 

 freely upon the surface, and which, judging by the analogy of 

 their general appearance, might be regarded as auditory. To 

 the sensory hairs of the second antennae likewise belong the 

 feathered hairs standing on the edges of the squama3 in the 

 higher Malacostraca ; 1 determined the presence of the group 

 ot sense-cells belonging to each of these hairs in the case of 

 My sis , Siriella, ISijuilla^ Faliemon, and Astacus. 



b. Sense- Organs of the Mouth-parts. 



As I have found in Myriapods and Insects sense-organs in 

 the buccal cavity and upon the mouth-parts which, according 

 to their position and form, were best interpreted as organs of 

 taste, it was a natural idea to search for such sense-organs in the 

 Crustacea also in the region of the mouth-parts. I was able 

 to determine that in all the species I examined, belonging to 

 the most widely different orders and families, the mouth-parts 

 always bear a large number of sensory hairs of various shapes, 

 generally feathered and pointed at the tip, which I would 

 regard as tactile bristles : I was never able to find hairs, 

 however, which could be compared with the olfactory tubes 

 of the anteima', or which, in consequence of their general 

 appearance, could be interpreted as gustatory or olfactory 

 organs. In the cases where the mandible carries a palp this 

 organ exhibits at the tip a large sensory field beset with many 

 hairs, e. g. in Astacus; in both i;airs of maxillae of all Crus- 

 tacea sensory hairs are closely packed on the exo- and endopo- 

 dites as well as on the lobes. In the case of Astacus I further 



* I may remind the reader that the second aiiteuna' may be atrophied 

 iulo a stump, e, <j. iu I'hroniina. 



