3G4 MEMOIttS OF THE NATIONAL ACADEMY OF SCIENCES. 



and those of the first and second thoracic legs. The eudopodites of the maxillipeds are as before. 

 The eudopodite of the first thoracic leg, which was represented in stage three by a rudimentary 

 bad, now appears to be entirely wanting. The second thoracic linib, which in stage three was 

 represented by a bilobed bnd, now consists of a basal joint, with a large, functional, plumose 

 exopodite and a rudimentary, bud-like endopodite. Between this appendage and the base of the 

 fully developed fifth thoracic limb there is a row of buds to represent the third and fourth thoracic 

 limbs, which became developed after the next molt. The fifth is about as it was in the preceding 

 stage, and it carries no trace of an exopodite. The abdomen is about as before, except that the 

 endopodite of the- sixth abdominal appendage, the only one yet represented, is now fully devel- 

 oped and fringed like the exopodite by long, plumose, swimming hairs. The telsou has becomjs 

 elongated and narrow, and the spines upon its posterior end are much smaller than before. 



THE FIFTH LARVAL STAGE. 



None of the figures of the larva; of other species exactly represent the larva of Alpheus minor 

 after the next molt. The eyes are now partially covered by the carapace, and the swimming 

 organs are the seven pairs of fully developed exopodites belonging to the three pairs of ruaxillipeds 

 and the first four pairs of thoracic legs. At this stage these four pairs of appendages reacquire 

 their endopodites, and the anterior end of the body is similar to that of the larva shown in PI. xxi, 

 Fig. 1, from which, however, it differs greatly as regards the telsou and the sixth abdominal ap- 

 pendage. The first five abdominal appendages are nou represented by buds like those shown in 

 PI. xxi, Fig. 1, and in PI. xix, Figs. 1 and 2, but the terminal portion of the abdomen is nearly like 

 that of Fig. 3 in PI. xx. The telson is greatly elongated, narrow, and its terminal spines are 

 very small. 



THE OLDER LARVAL STAGES OF ALPHETJS MINOR. 



During the successive molts the abdominal appendages become fully developed, the eyes be- 

 come completely covered by the anterior edge of the carapace, the antennre become elongated, the 

 autennnle develops a scale, the swimming exopodites of the maxillipeds and thoracic legs disap- 

 pear, these appendages assume their adult form, and acquire gills, aud the animal gradually be- 

 comes like the one shown in PL xx,,Fig. 2, which is a young Alpheus of another species. 



THE METAMORPHOSIS OF ALPIIETJS HETEROCHELIS FROM THE BAHAMA ISLANDS. 



Ill the Bahama Islands this species passes through a series of stages which, except for a few 

 minor differences of detail, are exactly like those in the life history which lias just been described. 



This fact is remarkable when it is known that the life history of the same species is very 

 different at Beaufort, North Carolina, and that Packard has described still another life history 

 for specimens of the same species which he studied at Key West. 



FIRST LARVAL STAGE. 



The Bahama specimens hatch from the egg in the stage shown in side view in Fig. 1 of Pl.xviil. 

 As this larva agrees in all details of its structure with the first stage of Alpli-eus minor shown in 

 PI. xvii, Fig. 2, already described, no further description is necessary. 



THE SECOND LARVAL STAGE. 



Like Alpheus minus the Bahama specimens of Alpheun keterochelis molt within a few hours 

 after hatching, but they undergo no essential change, and PI. xvi, Fig. 2, exhibits all the essential 

 characteristics, although this figure was drawn from a specimen of Alplieus minor. 



The most noteworthy specific difference is in the relative length of the marginal spines of the 

 telson. In the first and second larval stages of both species there are eight pairs of spines, one 

 pair on the outer edge and seven on the posterior edge, as shown for Alplieits minor in PI. xvi. Fig. 2, 

 and for Alphtus JieterncJielis in PI. xvi, Fig. 3. In both species the pair next the median line are 

 rudimentary and the next pair very small, but the three which arise from the rounded angle of the 



