[529] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 235 
developed into long locomotive appendages, somewhat like the external 
maxillipeds of the first stage of the young lobster. While yet in the free- 
swimming condition the cephalothoracic legs are developed, the maxilli- 
peds assume the adult form, and the abdominal limbs appear. The 
young of these shrimp are very much smaller than the young of the 
lobster, but they remain for a considerable time in this immature state, 
and were very frequently taken at the surface in the towing-net. 
The young of Crangon vulgaris are hatched in the neighborhood of 
Vineyard Sound, in May and June, and arrive at the adult form before 
they are more than 4 or 5™™ long. Specimens of this size were taken at 
Wood’s Hole, at the surface, on the evening of July 3. Later in the 
season much larger specimens were frequently taken at the surface 
both in the evening and day-time. 
The young of Palemonetes vulgaris did not appear till near the middle 
of July. Soon after hatching, the young are 3™™ long. The cephalo- 
thorax is short and broad with a slender spiniform rostrum in front, an 
enormous compound eye each side at the anterior margin, and a small 
simple eye in the middle of the carapax. The antennule are quite rudi- 
mentary, being short and thick appendages projecting a little way in 
front of the head; the peduncle bears at its extremity a very short ob- 
tuse segment representing the primary flagellum, and inside, at the base of 
this, a much longer plumose seta. The antenne are slightly longer, 
than the antennul; the short peduncle bears a stout appendage, corre- 
sponding to the antennal scale, the terminal portion of which is articu- 
lated and furnished with long plumose sete, and on the inside at the base 
of the scale, a slender process corresponding to the flagellum, and ter- 
minated by a long plumose seta. The first and second pairs of maxille 
are well formed and approach those of the adult. The three pairs of 
maxillipeds are all developed into powerful locomotive appendages ; the 
inner branches, or endognathi, being slender pediform appendages ter- 
minated by long spines, while the outer branches, or epignathi, are long 
swimming appendages like the swimming branches of the legs of the 
young lobsters in the first stage. Both branches of the first maxillipeds 
are considerably shorter than those of the following pairs, but otherwise 
like them, and the inner branch of the second pair is somewhat shorter 
than that of the third, but its outer branch is about as long as that 
of the third pair. The five pairs of cephalothoracic legs are wanting 
or only represented by a cluster of minute sack-like processes just behind 
the outer maxillipeds. The abdomen is long and slender, wholly with- 
out appendages beneath, and the last segment is expanded into a short 
and very broad caudal lamina, the posterior margin of which is truncate 
with the lateral angles rounded; these angles each bear three, and the 
posterior margin itself eight more stout plumose sctz, the sete of the 
posterior margin being longer than those upon the angles, and separated 
by broader spaces in which the margin is armed with numerous very 
small set. They arrive at the adult form before they are more than 5™™ 
17 v 
