332 MEMOIRS OF THE NATIONAL ACADEMY OP SCIENCES. 



After the fourth moult the larva passes into the fifth larval stage, when it resembles Fig. 1 of 

 PI. xxi, so far as concerns the anterior end of the body, from which it differs greatly as regards 

 the telson and uropods. The eyes are now well covered by the carapace, and the swimming 

 organs are the seven pairs of exopodites belonging to the three maxillipeds, and the first four 

 thoracic limbs. The first five pairs of abdominal appendages are now represented by buds, like 

 those shown in PL xxi, Fig. 1, but the telson and uropods are nearly like those of Fig. 3, in PL 

 xx. The telson is narrow and much elongated, and its marginal spines are very small. 



During the moults which follow, the abdominal appendages become fully developed, the eyes 

 become completely covered by the carapace, the autennule develops a scale, the antennae elon- 

 gate, the swimming appendages of the midbody disappear, these appendages assume their adult 

 form, and the animal gradually becomes like the young Alpheus shown in PI. xx, Fig. 2. 



This life-history is common to Alpheus minor at Beaufort and New Providence and Alpheus 

 normani and Alphem heterocheUs at New Providence, although the latter species presents a totally 

 different life-history at Beaufort. Before it hatches, this form, as shown in PL xx, Fig. 1, reaches 

 a degree of development which bears a general resemblance to stages two and three of the Bahama 

 form, with certain differences which are pointed out in the sequel. 



Immediately after hatching it assumes the form which is shown in PL xix, Fig. 2, and Fig. 1. 

 The animal has now all the somites and appendages of the adult, but all behind the maxillipeds 

 are rudimentary, and there is little power of locomotion. The first moult occurs in a few hours, 

 and the larva assumes the form shown in PL xx, Fig. 3, when it is no longer a larva but a young 

 Alpheus. The eyes are almost completely covered by the carapace, the ear is well developed, the 

 flagellum of the antenna has elongated, and the other appendages have assumed the adult form. 

 An older specimen is shown in PL XX, Fig. 2, and a still older one in PL xvii, Fig. 3. Careful com- 

 parison will show that no exact parallel can be drawn between any larval stage of this form and a 

 sluice of the first form, and that we have to do with something more profound than simple accele- 

 ration of development. The Bahama heterocheUs has, at first, three, then four, then five, and then 

 seven fully developed and functional exopodites, while the North Carolina form never has more 

 than three. As regards the thoracic region and the first five abdominal appendages the Beaufort 

 larva, at the time of hatching, is more advanced than the fourth larval stage of the Bahama form, 

 while the nropods are like those of the Bahama form at the time of hatching. 



In the latter the first and fifth thoracic limbs are the oldest, and the others appear in succes- 

 sion, while all five pairs appear together in the Beaufort form. In the Bahama form the uropods 

 appear before and in the Beaufort form after the others, and many minor differences show that we 

 have to do with profound modification of the life history rather than with simple acceleration. 



Packard's short account of the development of those specimens of this species which occu r 

 at Key West shows that these differ from the Beaufort specimens about as these latter differ from 

 the Bahama specimens. 



The second species is probably A. naulcyi, although Gue'rin's figure and description of this 

 form are not in accord with it in some important points. It is found in the Bahama Islands, living 

 in the tubes and chambers of two species of sponge, a green one and a brown one. Those found 

 in the green sponges have many small eggs, while those found in the brown sponges have only a 

 few largo eggs. The eggs from the green sponge hatch in the stage shown in PL xxi, Fig. 1. It 

 has rudimentary gills, the eyes are imperfectly covered, the antennules and antenna; are beginning 

 to assume their adult form, and the exopodites of the three pairs of maxillipeds are the chief organs 

 of locomotion, although all the appendages are represented. The abdominal feet are rudimentary, 

 however, and the nropods are covered by the cuticle of the telson. 



Very soon after hatching the larva moults and assumes the form shown in PL xxi, Fig. 2. The 

 eyes are more completely covered, the antennules and antennre are elongated, the thoracic limbs 

 have the adult form and the pleopods are all functional. 



In twenty-five or thirty hours after hatching it moults for the second time and passes into 

 the third stage, which is shown in Fig. 8. It is no longer a larva, but a young Alpheus, with all 

 the structural characteristics and pugnacious instincts of the adult. 



In a few cases the development of this species is still more accelerated, and a few eggs from 

 animals taken from the brown sponge hatched in the stage shown in Fig. 8, instead of the stage 



