[52!)] INVKRTKBRATE ANIMALS OF VINEYARD SOUND, ETC. 235 



developed iuto 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 vulgar is 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 mm 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 Palwmonetes vulgar is did not appear till near the middle 

 of July. Soon after hatching, the young are 3 mm long. The cephalo- 

 thorax is short and broad with a slender spiniforin rostrum in front, an 

 enormous compound eye eack side at the anterior margin, and a small 

 simple eye in the middle of the carapax. The antennulee 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 prim ary flagellum, and inside, at the base of 

 this, a much longer plumose seta. The antenna are slightly longer, 

 than the antennulse ; 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 setae, 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 maxillae 

 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 seta3, the seta3 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 setae. They arrive at the adult form before they are more than 5 mm 

 17 V 



