372 



THE INVERTEBRATA 



convention we have adopted (p. 333), the last somite of the true 

 thorax, but is usually reckoned as the first of the abdomen ; in the 

 female it is fused with the somite which succeeds it. Two free ab- 

 dominal somites and a telson, which bears two styliform, setose 

 caudal rami, complete the body. The somites of the thorax bear 

 limbs, which will be described presently. The 

 limbs of the somite of the genital opening are 

 present in the female only, and in her are re- 

 duced to the condition of small valves over 

 the openings of the oviducts. The abdominal 

 somites are without limbs in either sex. It 

 will be seen that the actual tagmata of Cyclops 

 are not the head, thorax, and abdomen, how- 

 ever 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. 250, 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) Fig 250. Mouth parts of 

 f ^ f , . 1 • 1 Cyclops, r rom bedgwick, 



are also uniramous; they stand immediately ^f^^j. ciaus. en. endopo- 



internal to the maxillae. The 2nd to ^th dite; ex. exopodite; md. 

 thoracic limbs, of which the 2nd stands on the mandible ;mx/maxillule; 

 head, are biramous, with broad, flat, spiny J^'^-" maxilla ;wj£:;).maxil- 

 rami (Fig. 249 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 antennules, and a swifter progression brought about 

 by the use of the swimming limbs (2nd to 5th pairs) of the thorax. In 



7nxp 



