some Freshwater Amphipods, 231 



NipJiargus as regards shape and have been able to determine 

 the foUowing forms : — 



Niphargus puteanus from Prague (PL XII. fig?. 23 & 24). 

 Sensory capsules 12 /x long and 4 //. broad, with usually a 

 short sense-hair ending in a tuft. Less frequently the sense- 

 hairs are simple, not branched. 



Niphargus elegans from Modena (PI. XII. fig. 22) . Sensory 

 capsules of the same form as in N. puteanus from Prague, 

 but the sense-hairs have forked ends with a long tuft on one 

 side. 



Niphargus tatrensis (Switzerland, fig. 26) ^ more strongly 

 swollen, with a simple sense-hair ending in a thread. 



A Niphargus from Lille lias very small sensory capsules 

 with sense-hairs of the paint-brunii type (fig. 27). 



In Niphargus Caspary^ from Munich, the sensory capsules 

 arc very pale, thin-walled, and short. They give rise to a 

 simple sliort sense-hair (fig. 28). 



Niphargus Kodiianus (Lough Mask in Ireland) is provided 

 with nearly spherical sensory capsules narrowed towards the 

 exterior and tufted sense-hairs (fig. 29). 



In Crangonyx suhterraneus, great numbers of which I have 

 been able to examine recently from the point of view of the 

 sense-organs now in question, the capsules are almost 

 cylindrical, longer than broad, the sense-hairs long, not 

 plumose ; sensory capsules 4-5 yu. long, sense-hairs 20 /x, long 



(fig. m). 



In Crangonyx covipactus^ from New Zealand, the sensory 

 capsules are very slender, terminating with a simple hair 

 (fig. 25). 



In all the species of Gommarus the capsules are, in the 

 main, spindle- sha]jed, slender, pointed exteriorly, not infre- 

 quently constricted in the middle, the sense-liairs shoit, not 

 plumose. The length of the capsules varies, according to the 

 species, from 16-22 /^ (figs. 20 & 21). The same details of 

 the form of the capsules apply, in general, to Balhyonyx also, 

 but the structures are much smaller and difficult to find 

 (figs. 17, 18, ^po, spo'). 



The internal structure of the sensory capsules diflfers from 

 that of the sensory brushes, but is the same in all genera, as 

 can be demonstrated with the greatest precision on the larger 

 forms occurring in the Gammarids. The proximal portion 

 of the cuticular wall of the capsule turns inwards and forms a 

 hollow axial stalk, to which the sensory seta is attached. In 

 some species of Gammarus and in Crangonyx the distal end 

 of the stalk, i. e. where the sensory seta arises, is thickened 

 into a little head. It is not difficult to make out that the 



