MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 365 



telson are much more nearly equal to the others in .!//>/. heterockelis than in Athens minor. If, 

 as seems probable, the triangular telson of the macrouran zoiia is a secondary modification of the 

 deeply furcated telson of a more ancient proto/,oea, then the first larval stages of Alpheus minor 

 are in this respect more primitive or protozoeau than those of Alpheus keterochelis. 



THE THIRD LARVAL STAGE. 



This is shown from below in PI. xvin, Fig. 2, and a comparison with Fig. 1 of PI. XVI will show its 

 very close resemblance to Alphata in in its at the same stage. The only essential difference between 

 them relates to the- rudimentary thoracic limbs. In both species the first thoracic limb has a 

 functional swimming exopodite and a rudimentary eudopodite, and in both the fifth thoracic limb 

 has a greatly elongated jointed cylindrical endopodite and no exopodite, but between these limbs 

 Alpheus hetcrochelis has buds to represent the other three pairs of thoracic limbs, while Alpheus 

 minor has buds for only one pair, and the other buds do not appear until after the next molt. 



THE FOURTH LARVAL STAGE OF ALPHEUS IIETEROCIIKLIS. 



This is shown from below in PI. xvin, Fig. 3, and there are no noteworthy differences between 

 it and Atyheus minor. 



THE LATER STAGES OF THE BAHAMA ALPHEUS HETEROCUELIS. 



% 



The transformation of the larva into the adult Alphens occupies a number of molts, and the 

 general character of the changes will be understood by the study of PI. xix and xx, although 

 these plates were drawn from Beaufort specimens of the species. 



THE METAMORPHOSIS OF ALPHEUS HETEROCHELIS FROM BEAUFORT, NORTH CAROLINA. 



As shown in PI. xx, Fig. 1, this, before it hatches from the egg, reaches a stage of develop- 

 ment which somewhat resembles stages two and three of the Bahama specimens. There are many 

 important differences however, and the stage in which it hatches is not directly comparable with 

 any stage in the life of the Bahama form, nor in that of Aipheus minor. Just before hatching it 

 has. like the Bahama form immediately after hatching, three pairs of fully developed swimming 

 maxillipeds, but it also has buds to represent all five pairs of thoracic legs. The antennary scale 

 and flagellum are much more advanced than they are at a much later stage in the Bahama form, 

 and the abdomen is much more distinctly segmented. The larva, immediately after hatching, is 

 shown in side view in PI. xix, Fig. 2, and in ventral view in Fig. 1. The autennule and antenna 

 are shown on a larger scale in Figs. 3 and 4, and the mandible and first and second maxilhe in 

 Figs. 5, 6, and 7 of the same plate. The animal now has all the appendages which are present in 

 the adult, but all behind the maxillipeds are rudimentary, although they all become functional 

 after the first molt, as shown in PI. xx, Fig. 3. 



The antennule, PI. Xix, Fig. 3, has a long cylindrical shaft made up of three joints fringed 

 with plumose hairs and terminating in an exopodite with sensory hairs and an eudopodite or 

 flagelluni, which is short and rudimentary but much longer than it is in the younger stages of the 

 Bahama specimens. The antenna, Fig. 4, presents even greater differences. The flagelluni is 

 about as long as the scale, and two jointed, while the scale itself is flat, although its tip still pre- 

 sents traces of a primitive segmented condition. It is, however, of little use in swimming, and in 

 fact the larva has at this stage only very feeble locomotive power. The eyes are stalked and 

 movable and almost completely uncovered. The mandible is simple and without a palpus, as 

 shown in Fig. 5. The first maxilla, Fig. 6, is very small, but apparently it is not rudimentary as 

 its two lobes carry cutting hairs. The second maxilla, Fig. 7, is a broad flat plate, very much 

 more developed than that of the newly hatched Bahama specimen shown in PI. XVI, Fig. 5. 



The three pairs of maxillipeds (PI. xix, Fig. 1) are almost exactly like those of the newly 

 hatched Bahama larva (PI. xvm, Fig. 1) or those of the Alpheus minor at the same, stage (PI. xvi, 

 Fig. 2), but the thoracic appendages (PI. Xix, Fig. 1) are entirely different, and the ventral surface 

 of the body is covered by a mass of limbs closely crowded, all pretty well developed, but all as yet 



