MORPHOLOGY OF THE COPEPODA. 289 



abortive feet of the fifth pair arise. The abdomen is^ in like 

 manner, identical, as regards the number of somites, with 

 the corresponding part in Cyclops. The first and second rings 

 are fused into a common, considerable-sized division, charac- 

 terised by the opening of the sexual organs. This is suc- 

 ceeded by three gradually smaller and smaller rings, the last 

 of which supports the fork with the caudal setae. The seg- 

 mentation of the body, therefore, in Nicothoe corresponds in 

 all respects with that of Cyclops. And precisely the same 

 may be said of the form assumed to represent the male 

 Nicothoe (fig. 3), which differs from the female of the same 

 length chiefly in the absence of the lateral thoracic projec- 

 tions. The external integument constitutes a thick chitinous 

 carapace, which in some parts is perforated by pore-canals, 

 disposed with bilateral symmetry. These are most clearly 

 seen in the frontal region, and exist, in fact, in the same 

 number, and arranged in the same manner, as they are in the 

 analogous situations in the female. These openings serve, as 

 perhaps do all the larger canals in the carapace of the Arthro- 

 poda, for the insertion of cuticular organs, and, in the present 

 case, of short, delicate chitinous filaments connected through, 

 the pores with the tissue of the matrix. Otherwise, also, the 

 carapace is by no means of uniform constitution, seeing that, 

 especially at the points of insertion of the limbs, various 

 thickenings of the chitinous covering, such as plates, ridges, 

 &c., afford firm supports to the lateral appendages. At the 

 fore part two spherical elevations of the carapace represent 

 the refractive parts of the visual apparatus, formed alike in 

 both sexes. This consists, as in the Saphirina, of a simple 

 cornea, but which in the present case is immediately suc- 

 ceeded by the pigment body with the percipient nervous part. 

 The other thickenings of the carapace are confined to the 

 ventral aspect of the cephalic and thoracic portions, on which, 

 owing to their constant and symmetrical arrangement, they 

 mark out definite regions to which, with as much reason as in 

 the various regions of the body in the Decapoda, special 

 designations might be assigned. The most complex of these 

 regions are the arese between the pairs of feet correspond- 

 ing with the so termed ventral vertebrae (Bauchwirbeln) of 

 Cyclops. 



Of the appendages, are first to be noticed the first pair of 

 antennae, which project from the fi'ontal region (fig. 3 a), and 

 which in both sexes possess the same number of joints, con- 

 sisting, as correctly represented by Kroyer, of ten rings. 

 Within their insertions spring the second antennae (fig. 4 b), 

 in the form of three-jointed appendages, which are formed 



