346 MEMOIRS OF THE NATIONAL ACA.DEMY OF SCIENCES. 



1883. In the Beaufort specimen (PI. ix) all the segments and appendages of the body are present, 

 and all of the latter are functional, excepting the first five pairs of abdominal feet, which are 

 rudimentary buds. The carapace is well developed, and termina,tes in front in a slender serrated 

 rostum, which is much shorter than in previous stages. The eyes are now large and prominent, 

 being mounted on long stalks. These organs, which are sessile in the protozoea, undergo marked 

 changes in both size and form in the course of development. They reach a maximum in a later 

 stage, and are correspondingly reduced during the passage from the latter to the adult. 



The inner antenna) are biramous ; the outer are reduced to a long narrow scale, armed with 

 bristles. The third pair of maxillipeds and first, second, third, and fourth pairs of thoracic legs bear 

 prominent swimming exopodites. The fifth pair of pereiopods characterize this larva by their 

 great length, and by the huge, paddle-shaped segment, which bears the small, terminal claw. 

 There is no exopodite to this appendage. The endopodites of the first, second, and fourth pereio- 

 pods are nearly equal ; the third longer. The first five abdominal segments are of equal size . 

 and, as stated, carry rudimentary feet. The sixth segment, however, is long and narrow, and has 

 the uropods well developed. 



D. Mysis stage. — The larva of stage C moulted into a form (PI. x) resembling the last, with the 

 addition of several important features. The inner antenniB consist, as before, of a segmented stem 

 with two terminal appendages. The first and third segments of the antennular stalk are short, 

 while the second is very long; spine nearly equal to length of basal segment; inner flagellum 

 very slender, shorter than the outer branch ; the proximal, thickened portion of which carries 

 several (three) bunches of sensory filaments. 



The antennal scale is as long as the antennular peduncle. The flagellum of the antennae now 

 appears as a slender filament, nearly twice the length of the scale. Possibly it is formed, as in 

 Peniims, from a bud-like remnant of the inner ramus of this appendage in the protozoi?a. The 

 third pair of maxillipeds and first to fourth pairs of thoracic legs are as in the jirevious stage, with 

 conspicuous exopodites fringed with sette. The endopodite of the fourth pair is longer than that 

 of the third ; the fifth pair are twice as long as the fourth ; and the breadth of the penultimate 

 segment is much reduced. 



The first, second, and third abdominal segments are equal ; the sixth is narrow, equal to length 

 of fourth and fifth. The telson is narrow, tapering, three times as broad at base as at apex; the 

 uropods are one-fourth larger than telson. Pigment is found as before, in the extremities of the 

 segments of the appendages. Large spots also appear on the abdomen and eyes. 



E. Mastiiioints stage. — On June 15 an older larva than the one just described was obtained in 

 the ocean outside the harbor at Nassau. It agrees in the main with the mastigopns of Sergestes. 

 The carapace ends anteriorly in a short spine or rostrum, which is bent up at an angle of about 40 

 degrees with the body. The eyes are mounted on very long naked peduncles. Both pairs of 

 antennai are biramous. The outer flagellum of the first or inner pair of antenna; is the longest (PI. 

 XI, Fig. 20), and it bears four or five bunches, containing in all about a dozen sensory filaments. 

 The inner branch is a bud. The second antennse extend as far forward as the joint of the first 

 pair, where the inner flagellum is given off'. The flagellum of the second pair is wound into a 

 short spiral coil. 



The exopodites of the second pair of maxillipeds are rudimentary (PI. xi, Fig. 31). The third 

 maxillipeds are now the stoutest appendages, and equal in length the third pair of thoracic limbs. 

 The first and second thoracic legs are slender; the third pair is the longest and the* terminal seg- 

 ment is bifid; the fourth is a short two-jointed rudiment; the fifth, corresponding to the huge 

 oar-like appendage of stage C, is reduced to a bud. It thvs appears that, as in the Sergestids, the 

 Jast two jMirs of walldng legs are shed after the mysis period, to be reconstructed again in the masti- 

 gopvs stage. 



All the abdominal appendages are functional. (PI. xi, Fig. 27.) The last segment of the abdo- 

 men is nearly equal in length to the three preceding. It is laterally compressed, and more nearly 

 resembles the adult form. In the act of swimming this larva carries the abdomen bent at nearly 

 a right angle to the rest of the body. It is colorless, excejiting areas of red pigment at the bases 

 of the abdominal feet, and spots on the lower portions of the antenn.'e ami eye-stalks. There is 

 also a transverse band of the same color on the anterior part of the carapace. 



