88 THE VOYAGE OF H.M.S. CHALLENGER. 



from the telson, altliougli its appendage is represented by a minute bUobed bud. This 

 larva therefore has all the appendages of the adult, either functional or represented by 

 buds, and all the somites of the hind body except the sixth abdominal. The outer ramus 

 of the flagellum of the first antenna is now bilobed, and the flagellum of the second 

 antenna is represented by a bud, aud the ocular somite is distinct and movable. The 

 rostrum is a little less than half as long as the carapace, aud the labrum is stdl farther 

 back. The width of the carapace between the bases of the antero-lateral spines is |^| of 

 its width between the bases of the postero-lateral spines, and the carapace with the 

 rostrum makes up almost exactl}'- half of the total length (xWxr)- ^^ other respects this 

 larva closely resembles No. 3. 



Larva No. 5, 17^-^ mm. long, is shown in PI. IV. fig. 6. The sixth abdominal 

 somite is still absent, and its appendages and those of the three last thoracic somites 

 rudimentary, although those of the third, fourth, and fifth thoracic somites have assumed 

 nearly their final form, and the first antenna has its three-jointed flagella. 



Although actually longer than that of No. 4, the rostrum is now relatively much 

 shorter, and only about one-fourth Oj^) as long as the carapace, and the distance from 

 its base to its tip is less than one-half (^|) of the distance from its base to the tip of the 

 labrum. 



The carapace is still shorter, as compared with the hind body, and with the rostrum, it 

 now makes up less than half (iVcmj) of the total length, although its lateral edges are still 

 straight, and its triangular shape is still retained. The greatest change is in the length 

 of the telson, which is now nearly twice as long as wide. 



Larva No. 6, 42^ mm. long, is shown in PI. VL fig. 3. It has all the somites 

 and appendages of the adult, although the sixth pair of abdominal appendages are 

 rudimentary. The carapace is still more elongated, and although the rostrum is actually 

 longer than it was in stage 5, it is much shorter both as compared with the total length 

 of the body of which it now makes j-§^, and also as compared with the carapace, which 

 is more than five times (%°o*) ^^ -^^ng as the rostrum. One of the most prominent 

 characteristics of the fully grown Alima gracilis is the great distance of the mouth from 

 the anterior end of the body, and in larva No. 6 the length of the rostrum is little more 

 than one-fourth (^) the distance from its base to the tip of the labrum. The carapace 

 including the rostrum makes a shghtly smaller portion of the total length (i^%) than at 

 stage 5, aud its lateral edges are no longer straight but are incurved near their posterior 

 ends, so that there is no increase in width in the posterior third of the carapace. 

 In the still older larva figured by Claus, this peculiarity is still more marked, and the 

 broadest part of the carapace is some distance in front of its posterior margin ; this is 

 more emarginated in stage 6 than it is in younger larvae, and it crosses the middle of 

 the sixth thoracic somite. The telson is still more narrow and elongated, and the sub- 

 median spines (PI. VI. fig. 3), which have become more and more closely approxi- 



