18 BE1TTSH COI'EPODA. 



last but one ?) abdominal segment. The hinder por- 

 tion of the alimentary canal is perhaps also uriniferous, 

 but there exist near the bases of the foot-jaws other 

 glandular organs, which may have a renal function. 

 In the males of parasitic Copepoda the digestive canal 

 disappears entirely. 



RESPIRATION. If we are right in assigning to certain 

 appendages of the mouth-apparatus (to which refer- 

 ence has been already made; see pp. 10, 11 *) a branchial 

 function, then we cannot altogether assent to the 

 commonly - received belief that respiration in the 

 Copepoda is carried on entirely by the dermic and 

 intestinal surfaces of the body, without the interven- 

 tion of any specialized respiratory apparatus. A sub- 

 rhythmic contraction of the hinder extremity of the 

 gut has, however, been noticed by Mr. Hartog in 

 several Copepoda (Cyclops, Diaptomus, Canthocamp- 

 tus), and by several observers in other Crustacea (e. g. 

 Astacus, Limnadia, Daphma) : this is, no doubt, a 

 respiratory movement. 



CIRCULATION. In many Copepoda no special circu- 

 latory organs have been found ; but in some there is 

 a tubular heart, situated in the last thoracic segment, 

 which drives forward the blood by a short vessel to 

 the brain and anterior parts of the body, the blood 



* There can be no doubt that these setiferous plates are homologous 

 with the structures called in the Ostracoda branchial lamince by G. O. Sars. 

 But they do not appear to have any special internal circulation of the 

 vital fluids, and if their function be branchial, they must act only by 

 propelling waves of aerated water over the neighbouring surfaces. It 

 is, pei'haps, on the whole, most probable that the currents produced by 

 these ciliated appendages are subsidiary to nutrition rather than to 

 respiration. 



