MEMOIRS OP THE NATIONAL ACADEMY OF SCIENCES. 367 



cbeliie, aud the eyes were nearly sessile. In this case also there seems to be modification as well as 

 acceleration, as Packard says that there were only five 'pairs of abdominal feet and that these were 

 well developed. It may seem to some that the fact that these three forms present such great aud 

 constant differences in development is a reason for regarding them as three distinct species, but, 

 whether we hold that they belong to cue, two, or three species, they will still furnish proof of the 

 existence of profound modifications in the life histories of adults which have remained almost 

 exactly alike. 



Careful and minute comparison between adult specimens from Beaufort and Nassau showed 

 the closest agreement in nearly all particulars (v. Chap, v, Pt. First, Section n), and it has there- 

 fore seemed best for us to regard them as belonging to a single species; the more so since our 

 discovery that different individuals of another species found at Nassau (Alpheus saulcyi) differ from 

 one another during their larval tages in somewhat the same way that the Beaufort specimens of 

 heterochelis differ from the Bahama specimens. 



Alpheus minor aud Alpheus heterochelis are very distinct species. The adults have diverged 

 from one another so far that one could not possibly be mistaken for the other ; yet the life history of 

 the Bahama heterochelis is so exactly like that of Alpheus minor, both at Beaufort and in the 

 Bahamas, that the same figures of the early stages will serve for both ; for the larval stages of 

 heterochelis have undergone local modifications, while the adults have remained almost absolutely 

 unchanged, except as regards the reproductive elements aud their product. 



t SECTION V. LARVAL DEVELOPMENT OF ALPHEUS SAULCYI. 



An egg of Alpheus saulcyi just ready to hatch is shown in PI. xxi, Fig. 5. The large claws are 

 plainly visible through the transparent shell. The auteume are folded back alongside the body, 

 while the abdominal aud closely packed thoracic appendages are directed forward. The telson 

 overlaps the head. 



First larva (length, = -^ inch). Fig. 1 shows the larva as it is just hatched. It belongs to 

 the variety found in the brown sponges. The various parts may be seen more highly magnified in 

 PI. xxi, Figs. 4, 6, 7,9, and PI. xxri, Figs. 1-8, 12. In both varieties the animal hatched as a schizo- 

 pod, loosely infolded in a larval skin, but uot invariably, as I have noticed that in one or two cases, 

 where females of the lougicarpus with very few, perhaps half a dozen eggs, produced young, the 

 metamorphosis was completely lost, the larva; being in a stage corresponding to that usually at- 

 tained after the second molt aud represented in PI. xxi, Fig. 8 This is referred to again at 

 the end of the section. 



To return to the first larva (PI. xxi, Fig. 1) ; this is fifteen one-hundredths of an inch long. It 

 is semi-transparent and colorless, except for spots of characteristic red and yellow pigment sprinkled 

 freely on the abdomen, the telsou, and appendages. Rudimentary gills are present and a remnant 

 of uuabsorbed green yolk is conspicuous in the stomach. The carapace covers the bases of all the 

 thoracic appendages but the last pair. It is produced forward into a short simple spine, the ros- 

 trum, which extends between the eyes. There is a rudiment, on either side, of the ocular spines 

 (PI. xxii, Fig. 6), which soon grow forward and give to the front the characteristic trident shape. 

 The eyes project forward, only the extreme base of the stalk being covered by the carapace. A 

 median eye or ocellus is present just below and between the bases of the lateral eye stalks. 



Both pairs of auteunre are biramous and jointed. The auteuuules (Fig. 8) consist of a stout 

 peduncle, a short eudopodite, and a shorter bud or outer branch, which bears several bunches of 

 sensory filaments. The peduncle is composed of three segments, as in the adult; the basal joint 

 being four times the length of either of the other two, and bearing on its outer side a rudimentary 

 aural scale. The upper margin of each joint carries one or more plumose hairs. The auteuure 

 (PI. xxu, Fig. 7) are formed on the adult plan. There is an inner auteimal stalk consisting of 

 two joints, bearing a rudimentary flagellant, and an outer scale or exopodite. The distal margin 

 of the exopodite is garnished with plumose hairs and carries a short outer spur. 



The mandibles (Fig. 12, drawn from a larva after the first moult) arc deeply cleft, as in the adult. 

 The outer branch is deutated at its distal end aud carries a palpus. The first maxilhe (Fig. 0, 



