Development of Estheria Packardi. 15 



As the postlarval development on the whole proceeds 

 rather gradually, without any strongly marked changes, only 

 some few stages need be described in detail. 



First postlarval stage. 



(PL III, fig. 1). 



Though this stage immediately succeeds the last larval 

 one, being only marked off from it by a single exuviation, 

 very considerable changes have taken place in the orga- 

 nisation of the animal, which now presents itself under a 

 rather different appearance. Whereas in the larval stages, 

 owing to the lateral extension of the antennæ and mandi- 

 bular feet, the animal, when brought under the microscope 

 in a small quantity of water, invariably turns its dorsal or 

 ventral face to the observer, it is now found to assume a 

 lateral attitude, it being rather difficult to get a dorsal or 

 ventral view of the animal. This is chiefly due to the 

 transformation of the carapace, as also to a somewhat diffe- 

 rent direction of the antennæ. On the whole, the animal 

 now exhibits a more compressed form, whereas in the larval 

 stages it looks on the contrary somewhat depressed. Of 

 exclusively larval organs some remnants are still found, though 

 in process of degeneration. Thus the antennæ exhibit at the 

 base posteriorly a conical projection, not found in the suc- 

 ceeding stages. This projection is the rudiment of the 

 peculiar bifurcate masticatory process, mentioned in the larva 

 as a most efficient auxiliary organ for alimentation. 

 Moreover, a rudiment of the mandibular feet is still found 

 appended to the outer side of the mandibles, but both 

 these appendages are now quite useless, and have therefore 

 lost their bristles, being also greatly reduced in size. 



