32 BRITISH FOSSILS. 



thorax ; or, 2, they have remained undeveloped at the posterior 

 end of the thorax ; or, 3, the two somites which are so closely 

 united together as to appear as one segment, commonly regarded as 

 the first of the abdomen, belong in reality to the thorax. This 

 view might be supported by the position of the reproductive 

 apertures which open behind the second of these somites, that is, 

 on this hypothesis, in that position immediately behind or at the 

 posterior part of the thorax, which is so common to them in 

 Edriophtlialmia, Pcecilopoda, and male Podophthalmia. If this 

 view be correct, (but I would expressly state that it is put forth 

 only tentatively,) it is the abdomen alone, which is shorn of its due 

 proportions in Copepoda. 



Such is the structure of a typical copepod. The modifications 

 observable in the order, of importance for my present purpose, 

 affect, Istly, the form of the body ; 2ndly, the character of the eyes ; 

 3rdly, the form of the antennules and antennae ; 4thly, that of the 

 lab rum and metastoma ; 5thly. the number of the thoracic 

 appendages. 



1. The body usually has a general resemblance in outline to 

 that of Calanus, the abdominal somites commonly presenting a 

 marked and immediate diminution in transverse diameter when 

 compared with those of the cephalo-thorax. In the beautiful 

 Sapphirince. (Plate XVI. fig. 19), however, the passage from the 

 cephalothoracic to the abdominal somites is quite slow and gradual. 



2. In most Copepoda the eyes are so closely united as to 

 appear single, and the region of the carapace which overlies them 

 is not so modified as to deserve the name of a distinct cornea. But 

 in the genus Sapphirina (Plate XVI. fig. 19), there are two small 

 single eornese approximated together in the middle of the dorsal 

 surface of the carapace ; and a still more interesting modification of 

 the visual organs is presented by Corycceus (Plate XVI. figs. 8, 9). 

 Here two great, oval, spectacle-like, corneas are situated, one on each 

 half of the anterior rounded margin of the carapace. 



3. The antennules and antennas vary very much in form. In 

 many Copepoda they are so constructed as to subserve prehension, 

 either for sexual or other objects. The antennules are thus 

 specially modified in the males of Pontella and Cyclops, while in 

 CoryccBUS these organs remain simple ; but the antennae (III/) are, in 

 both sexes, converted into formidable weapons. It will be observed, 

 however, that prehension is effected by the folding of the ultimate 

 upon the penultimate joint, not by the biting of the apex of the 

 ultimate joint against the prolonged distal angle of the penul- 



