COPEPODA 



333 



domlnal somites are without limbs in either sex. It will be seen that 

 the actual tagmata of Cyclops are not the head, thorax, and abdomen, 

 however the limit between thorax and abdomen be fixed, but are a 

 cephalothorax of eight somites (including the preantennulary), a mid- 

 body (sometimes, but unsuitably, named the '*metasome") of three 

 somites, and a hind body or " urosome " of five somites and the telson. 



On the head, the median eye is well de- 

 veloped. The antennules are long, uniramous, 

 provided with sensory hairs, divided into 

 seventeen segments, and in the male bent as 

 hooks to hold the female. The antennae are 

 shorter, slender, uniramous, and four-jointed. 

 The mandibles (Fig. 239, md.) have a toothed 

 blade (gnathobase) projecting towards the 

 mouth and a papilla, bearing a tuft of bristles, 

 which represents the palp. The maxillules 

 have a large gnathobase and small endopodite 

 and exopodite. The maxillae are uniramous. 

 The maxillipeds (first pair of thoracic limbs) 

 are also uniramous ; they stand immediately 

 internal to the maxillae. The 2nd to ^th 

 thoracic limbs, of which the 2nd stands on 

 the head, are biramous, with broad, flat, 

 spiny rami (Fig. 238 B). The protopodites 

 of each pair are united by a transverse plate 

 or "copula" so that they move together in 

 swimming. The thoracic appendages of the 

 6th pair are small and uniramous. 



The swimming of Cyclops is of two kinds — • 

 a slow propulsion by the antennae and anten- 

 nules , and a swifter progression brought about 

 by the use of the swimming limbs (2nd 

 to 5th pairs) of the thorax. In the more primi- Fig. 239. Mouth parts of 

 tive, pelagic copepods (Calanus, etc.) which Cyclops. From Sedgwick, 



have biramous antennae and biramous palps ^^^^^ C^^^^- ^«- endopo- 

 . fi 1 1 11 1 dite; ex. exopodite: ma. 



on the mandibles, the antennules do not take mandible; mx.' maxillule; 

 part in swimming. Such copepods /(?^^ by mx." maxilla; mxp.maxil- 

 an automatic straining of particles from the liped. 

 water, though their apparatus for this purpose (see below) is very 

 different from that of the Branchiopoda. Cyclops, on the other hand, 

 in a manner of which the details are not understood, seizes its food 

 particles from time to time. 



The alimentary canal is of much the same nature as that of Chiro- 

 cephalus but without mid gut diverticula. It possesses well-developed 



mxp 



