MUSEUM OF COMPARATIVE ZOOLOGY. 313 
and outer branches, which are now two- and three-jointed respectively. 
'l'he 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 (Pl. II. Figs. 2, 3, 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 tho rudiments of 
the following two pairs in the shape of small double sacs (Pl. 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 (PL EL Fig. 3, 
XIX). They have the shape of oval plates lying within the sides of 
the triangular telson. 
Third Larval Stage (Pl. II. Figs. 5 —9). — Larva in this stage of 
development were frequently taken free-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 swimmercts, renders this stage 
distinguishable at a cursory glance from cither 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 antenne are no longer simple, the rudiments of the 
inner flagellum having appeared as a small bud (Pl. IT. Fig. 5, 7, v 2) 
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 (Pl. II. Fig. 5, Z, 7 e). 
In the second pair of antenne the inner branch (Pl. II. Fig. 5, 77, 
rt), which becomes the chief part of the antenna in the adult, has 
