4 BRITISH COPEPODA. 



placed the median eye, often single to all appearance, 

 but really composed of two closely approximated 

 lateral eyes, embedded in a mass of black or crimson 

 pigment. 



The head and the first thoracic segment are usu- 

 ally fused together, a fact which may be recognised 

 by the position of the first pair of swimming feet 

 (the first thoracic appendages), these limbs being 

 generally fixed to the hinder part of the first body- 

 segment, which is thus seen to be composed of all 

 the cephalic, and the first of the thoracic, somites. 

 In some cases a transverse indentation may be noticed, 

 probably a trace of the " cervical suture " which is so 

 conspicuous a feature of the carapace in Crayfishes 

 and Lobsters. Instances are frequent, however, in 

 which the head is quite distinct from the thorax. 



Theoretically, the Copepoda, like other Crustacea, 

 are composed of twenty or twenty-one somites 

 (twenty-one according to most authors, but twenty 

 if we follow Huxley, who does not look upon 

 the telson or last abdominal segment as a true 

 somite), the entire series not being developed, how- 

 ever, in any one animal. Sometimes one or many 

 of the somites are suppressed, at other times several 

 are united into one segment, the real nature of 

 which is rendered evident by the attachment to it of 

 several appendages, each pair indicating the position 

 of an anchylosed somite. Probably in no case 

 amongst the Copepoda can more than sixteen or 

 seventeen somites be recognised by enumeration 

 either of appendages or segments. The somitic appen- 



