MUSEUM OF COMPARATIVE ZOOLOGY. 313 



and outer branches, which are now two- and three-jointed respectively. 

 The second and third pairs retain the same number of segments as 

 before. 



The anterior of the two pairs of double sac-like appendages, which lay 

 behind the third pair of maxillipeds in the last stage, have disclosed a 

 pair of two-branched swimming-feet (PI. II. Figs. 2, '6, 4, IX). These 

 swimming-feet, which ultimately become the anterior pair of chelipeds 

 in the adult, have about the same structure as the antecedent maxilli- 

 peds, but are somewhat shorter. 



At the base of the appendages just mentioned are the rudiments of 

 the following two pairs in the shape of small double sacs (PI. II. Fig. 4, 

 X, XI). The second pair are very small, and appear now for the first 

 time. 



There is still no trace of the abdominal limbs, except in some speci- 

 mens about to moult, in which the last pair (swimmerets) are visible 

 through the transparent integument within the caudal fin (PI. II. Fig. 3, 

 XIX). They have the shape of oval plates lying within the sides of 

 the triangular telson. 



Third Larval jStage (PI. II. Figs. 5-9). — Larvoe in this stage of 

 development were frequently taken frea-swimming at the surface of the 

 water, both at Newport and Wood's Hole, in July and early August. 

 From their slight advance upon the preceding form, I have little doubt 

 of their coming from it by a single moult, although I did not succeed in 

 raising this stage in confinement. 



In general form the larva still bears a close likeness to the stage last 

 described. The telson, however, has lost its broad, triangular shape, 

 and now, flanked by the free, bilobed swimmerets, renders this stage 

 distinguishable at a cursory glance from either of the preceding ones. 



In addition to the spines seen on the carapace in the second larval 

 stage, there is now a minute one on the anterior border, below the 

 supra-orbital spine. This seems to correspond to the antennal spine in 

 the adult. 



The first pair of antenna) are no longer simple, the rudiments of the 

 inner flagellum having appeared as a small bud (PI. II. Fig. 5, /, r i) 

 from the inner side of the distal end of the second segment. It is 

 tipped by a long seta. The segment which terminated the simple an- 

 tennule of the previous stage now appears as the rudimentary external 

 flagellum (PI. II. Fig. 5, /, r e). 



In the second pair of antenna? the inner branch (PI. II. Fig. 5, II, 

 ri), which becomes the chief part of the antenna in the adult, has 



