10 G. 0. Sårs. 



ated than in the preceding stage, and the posterior 

 division has now assumed a more conical form, being con- 

 siderably tapered in its outer part. At the base, it exhibits 

 on each side a rather conspicuous swelling, indicating the 

 place where subsequently the lateral parts of the carapace 

 are to be formed, but is otherwise as yet quite simple. The 

 furcal projections have however become considerably more 

 elongated than in the preceding stage, forming 2 pointed 

 lappets separated by a deep sinus. 



As to the limbs, at least one very conspicuous change 

 has taken place. This change affects the masticatory pro- 

 cesses of the antennæ, which now appear considerably 

 stronger, and have divided at the end in a fork-like manner 

 into 2 somewhat unequal and densely ciliated points. It 

 is evident that this modification renders these processes still 

 more suitable as auxiliary organs for the procuring of food. 



Fourth larval stage. 



(PL I, figs 6 & 7). 



Though this stage does not appear to be marked off 

 from the preceding one by any true exuviation, it is, how- 

 ever, pronouncedly distinguished by the first apparition of 

 the carapace and of the anterior pairs of legs, these parts 

 having developed inside the larval' skin. 



The carapace, or rather the first intimation of such, 

 presents itself as a rather small, semilunar fold extending 

 dorsally over the most anterior part of the trunk, and having 

 its posterior edge deeply emarginated in the middle (see 

 fig. 6). The lateral parts of this fold represent the valves 

 of the shell in the adult animal, and are not yet defined 



