some Freshwater Amphipods. 22 :» 



distal outer edge of the first joint in the space between the 

 large ordinary setse. In addition, tiiere are in the middle of 

 the same joint two further sensory brushes, accompanied by 

 a thicker ordinary seta, exactly as in Cmngonyx. 



In Bathyonyx also there are always two sensory brushes 

 in the middle of the first joint and four on the distal edge. 

 Their structure is the same as in Crangonyj-, Niphartjus, 

 and Gammarus. .Each sensory brush consists of a basal 

 cup or urn sunk into the fibrous inner cuticle. (This fibrous 

 inner cuticle is covered with a thin homogeneous outer 

 cuticle, PI. XL fig. U,c). 



From the cup there arises the stem of the seta, which, at its 

 distal end, is furnished with two lateral rows of fine hairs 

 (PI. XI. fig. 14). I have designated these sense-hairs in 

 Crangonyx as " quaking-hairs '' [Zitterhaare], because in the 

 living state they are found to be subject to periodical 

 vibratory movements, which ])oints to some definite sensory 

 action. The quaking movement of these hairs of Amphipods 

 is certainly worthy of remark, especially as it resembles 

 ciliary action, although produced in a diflferent manner from 

 the latter. The quaking of the sense-liairs reminds one 

 rather of the flame-cells [Zitterorgane] of the llotatoria, or 

 of the tufted hairs [Biischelhaare] which I have described in 

 Bothrioplana hohemica *. 



By the examination in profile of the transparent first 

 antenna it is easy to demonstrate that the sensory brushes 

 are su])plied with nerves from the antennal ganglion. Long 

 and fine processes from the ganglion-cells are connected with 

 special club-shaped cells, the short process from each of which 

 is spread out like a dish at the base of the cup from which the 

 seta arises (PI. XL fig. 14, ne). The structure of the ganglia in 

 the antennae of the Gammarids is, according to what I have 

 so far been able to demonstrate in Gammarus pulex^ &c., 

 very characteristic and deserves special attention from com- 

 parative nerve histologists. 



On the lower antennae the sensory brushes only occur 

 singly ; thus I have observed two on the second joint and 

 one each on the third and last joints of the same form and 

 size as on the first antennae. 



I only found the hyaline clubs, so-called olfactory clubs, 

 on one specimen (PI. XL fig. 3) ; they are very short, not 

 attaining the length of the joints, and therefore very ditiicult 

 to observe. 



* "Zur vergleich. Anatomie der Turbellarien," Zeit. f. wiss. Zool. 

 Bd. Ix, (lUCij. 



