COPEPODA. 



433 



343), the larva still resembles a Nauplius, and it is only after another 

 rnoult that it is transformed into the first Cyclops-like form. It 

 then resembles the adult animal in the structure of the antennse and 

 mouth parts, although the number of the appendages and the body 

 rings is smaller (fig. 342, c). The two last pairs of appendages already 

 have the form of short biramous swimming feet, and the rudiments 

 of the third and fouth pairs of swimming feet have made their 

 appearance as projections beset with setse. The body consists in this 

 stage of the oval cephalothorax ; the second, third and fourth thoracic 

 segments ; and an elongated terminal portion, which gives rise to the 

 last thoracic segment, and to all the abdominal segments by a pro- 

 gressive segmentation, and already terminates in the caudal fork. 



FIG. 344. Adheres percarum. a, Nauplius form, b, Larva in the youngest Cyclops stage; 

 Ef, Ef", maxillipeds. c, Female seen from the ventral side. Ov, Ovaries ; KD, cement 

 glands, d, The smaller male seen from the side ; Mxf, Mxf", maxillipeds. 



Many forms of parasitic Gopepoda, for example Lernanthropus 

 and Chondr acanthus, do not get beyond this stage of body segmenta- 

 tion, and obtain neither the swimming feet of the third and fourth 

 pairs, nor a fifth thoracic segment separate from the stump-like 

 abdomen; others, for example Achtheres, by the loss of the two anterior 

 pairs of swimming feet, sink back to a still lower stage (fig. 344). 



All the non -parasitic and many of the parasitic Gopepoda pass 

 in the successive moults through a larger or smaller number of de- 

 velopmental stages, in which the still undeveloped segments and 

 appendages make their appearance, and the appendages already 



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