214 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



end of each is reentrant or bowl-shaped, and the claw is attached 

 in the bottom of the bowl. It is very short and stout, with an 

 enlarged, bluntly rounded or conical tip; the base of the cone forms 

 a flange or barb around the claw and is reentrant at one point on the 

 ventral side (fig. 21). This claw is entirely without muscles and 

 therefore can not be moved, except as the whole maxilla moves. 



The two claws can be distinctly seen imbedded in the enlarged 

 proximal end of the attachment filament, and can be easily pried out of 

 the latter (fig. 19). The filament also is a hollow tube whose structure 

 corresponds exactly with that seen in the frontal region of the larva 

 in the preceding stage. And if we follow along to the distal end of 

 the filament, where it is attached (in this instance) to one of the 

 spines on the gill arch, we find there the mushroom-shaped enlarge- 

 ment which was so conspicuous in the free-swimming larva (figs. 27 

 and 38), There can be no doubt of the identity of the two struc- 

 tures. It often happens that the claws and the filament for some 

 little distance near them are covered with a mass of the adhesive 

 substance arranged in ridges or transverse wrinkles, as though some 

 of the contents of the tube had escaped when it was transferred from 

 the frontal margin (fig. 24). This is exactly what would be expected 

 and strengthens the proof of such transference. 



The maxillipeds retain their segmentation and have practically the 

 same structure as before. The only change has been that they have 

 migrated forward a little between the bases of the second maxillae, 

 so that now the two pairs of appendages are about on a level. 



The swijnming legs have greatly degenerated; they have dimin- 

 ished in size until oftentimes it is difficult to find them and they have 

 lost their plumose setse. They are now made up of a tiny basal joint 

 and two still more minute rami, each of which is tipped with two 

 short spines (fig. 28). They disappear entirely at the next molt. 

 The spines which represented the third pair of legs on the sides of 

 the third thorax segment in the free-swimming stage have entirely 

 disappeared. 



Total length of this second copepodid larva, 0.42 mm. Length 

 of cephalothorax, 0.30 mm. Width of same, 0.20 mm. Width of 

 second thorax segment, 0.10 mm. 



SEX DISTINCTION. 



The larvae show enough differences in this second copepodid stage 

 to enable us to distinguish the sexes. 



The male (fig. 25) is shorter and more stocky than the female; in 

 dorsal view the body is distinctly separated into two regions, a 

 cephalon subquadrilateral in outline and nearly half the entire length, 

 and the body proper, cylindrical in form, narrower than the cephalon, 

 and tapering backwards. Between these two regions is a strong 



