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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 47. 



ments which follow it in AcMJieres and Salmincola, but is the same 

 size or a trifle narrower in OlaveUa. The third and fourth segments 

 are about the same size and length in all the genera, but their relative 

 size compared with the cephalothorax or with the second segment 

 varies greatly. In general they are very narrow in AcMJieres and 

 Salmincola and very wide in ClaveUa. The last segment is a fusion 

 of the posterior portion of the thorax and the abdomen, and it carries 

 the anal laminae, which are variously armed with setae in the different 

 genera. The first antennae are four-jointed and extend directly out- 

 ward at right angles to the body axis in Salmincola and AcJitJieres; 



in ClaveUa they ap- 

 parently have fewer 

 joints and are turned 

 backward along the 

 sides of the carapace. 

 The second antennae 

 are biramose, the exo- 

 pod one -jointed and 

 tipped with a single 

 seta, the endopod two- 

 jointed and ending in 

 a powerful hooked 

 claw. The mouth- 

 tube projects downward and forward from between the bases of the 

 second antennae. It is made up of an upper and under hp, the lat- 

 ter grooved and fluted, overlapping the edges of the upper lip, and 

 consisting of two halves, which are often not entirely fused. The 

 mandibles are outside the base of the mouth-tube, one-jointed and 

 tipped with short setae; the first maxillae are also uniramose but 

 two-jointed and tipped with longer setae; the second maxillae are 

 stout, two-jointed, and tipped with a long and slender claw, bent 

 into a half circle; the maxillipeds are also stout, three-jointed, and 

 tipped with a stouter and straighter claw (fig. 14). Swimming legs 

 biramose, the basal joints broad and laminate, and furnished \\dth 

 powerful muscles, the rami small, one- jointed, and armed with long 

 plumose setae (fig. 15). 



As soon as this copepodid larva escapes from the egg it begins an 

 active search for a host. By means of its two pairs of swimmmg 

 legs it moves about actively in a more or less spiral path. ^ This 

 movement is kept up for 24 to 48 hours, and then relaxes, the 

 larva becoming so wearied that it can scarcely move at all. Conse- 

 quently it must find a host within this time or perish; if it is fortu- 

 nate enough to come in contact with the right kind of fish it fastens 



Fig. 14.— Copepodid larva of Clavella uncinata. a, Mandible; 



6, FIRST maxilla; C, second MAXttLA; d, MAXILLIFED. 



1 Fasten, Journ. Animal Behavior, vol. 3, 1913, p. 43. 



