The external apertures ure : — The openings of the 

 paired excretory organs at the base of the second an- 

 tennae, the mouth, the openings of the oviducts at the 

 base of the fifth or of the vasa deferentia at the base of 

 the seventh pair of legs, and the anus. 



There are nineteen pairs of appendages : — The first 

 and second antennae, the mandibles, the first and second 

 maxillae, the fused maxillipeds, the two pairs of gnatho- 

 pods (which with the first two pairs of perajopods are 

 directed forwards), five pairs of peraeopods, three pairs of 

 pleopods or swimmerets, and three pairs of uropods. 



The first or superior antennae (PI. I., fig. 1, and PI. 

 II., ant. 1) are nearly half as long as the body. Each con- 

 sists of a three-jointed peduncle or protopodite, bearing a 

 long flexible many-jointed flagellum or endopodite, and a 

 shorter similar secondary flagellum or exopodite (PI. I., 

 fig. 1, fl. sec). In G. _/Jw/e,'C the latter is very small, con- 

 sisting only of four joints; in G. locusta it is considerably 

 longer, consisting of eight or nine joints. In G. fulex 

 the first joint of the peduncle is shorter than the other two 

 combined, and the long flagellum is twice the length of 

 the peduncle; in G. locusta, the first joint of the peduncle 

 is as long as the other two combined, and, as in G. pule.v, 

 the long flagellum is twice the length of the peduncle, or 

 rather longer. Each joint of each flagellum bears small, 

 finely plumose setae, probably auditory in function (Sars 

 20). It was noted that specimens of G. 'pulex placed 

 in a cell and examined under the microscope twitched the 

 first antennae violently when the college clock struck the 

 hour,* though the rest of the body did not move. 



The second or inferior antennae (PL I., fig. 2) are 



shorter than the superior, and consist of a three-jointed 



■'- The note to which the first antennae were found to react was 

 B^ (240 vibrations per second) ; higher notes chimed by the same 

 clock had not the same effect. 



