some Freshioater AmpJiipods. 2155 



Between the two layers there is a hollow space, whether 

 artifically produced or not I am unable to decide. But 

 according to the known structure of the eye in Gammm-us 

 we should be dealing, in the lower pigmented layer of cells 

 arranged almost like epithelium, with retinula-cells, to which 

 also the outer pigment-masses belong, they being certainly 

 only separated by the unsatisfactory method of fixing. From 

 this it would seem that in Batliyonyx the retinula apparatus 

 was still retained, although the dioptric elements were 

 gradually destroyed. For the crystalline cones described 

 above must be considered as being in process of degeneration : 

 firstly, because they do not form a single compact eye, but 

 are only loosely scattered under the hypodermis, and, secondly, 

 because the actual substance of the normal crystalline cone is 

 gradually degenerating. 



Special investigation of the mouth-organs of Bathyonyx 

 shows that they resemble in form those of GrangonyXj exce[)t 

 that they are much more feebly developed, thus corresponding 

 to the general organization of Bathyonyx. The drawings of 

 the mandibles and their palps (fig. 4), of tlie maxilUe of the 

 first (figs. 5 & (j) and second pairs (rig. 7), and, lastly, of the 

 niaxillipedes (fig. 8) entirely support this conception. Tiie 

 palpi of the niaxillipedes are almost as long as the gnathopods, 

 which are also very weakly developed, especially the iiands, 

 which, under low magnification, can scarcely be distinguished 

 from the almost equally broad or even broader proximal joints 

 (carpopodites). The form of the hands of the gnathopods of 

 buth pairs reminds one of Crangonyx^ but in general in this 

 case, as in Crangonyx, there is some variability. In order 

 to show this I give in figs. 9-11 camera drawings of the 

 hands of tliree specimens. Figures 10 and 11 are shown 

 under the same and fig. 9 under a slightly higher magni- 

 fication. From a comparison of the three it is ap[)arent that 

 the only character common to all is that the hands of the 

 first pair are obviously broader and shorter than those of the 

 second pair. It can also be seen from the drawings that the 

 oblique outer edge of both hands is finely toothed and that the 

 armature of strung setse which is characteristic of the hands 

 of Gammarus, Crangonyx, and in part Niphargus (as I have 

 specially remarked in connection with Crangonyx) is entirely 

 absent in Batliyonyx. In other respects a slight variability 

 in the form of the hands is to be observed in all three cases, 

 which is also true of Crangonyx. A comparison of the form 

 of the gnathopod hands of the last-named genus, as I have 

 figured them in my paper (21, figs. 12-14), with those figured 



IG* 



