MEMOIRS OF THE NATIONAL ACADEMY OF SOIENCES. 367 



cheliP, and the eyes were nearly sessile. In tLis case also tliere seems to be modification as well as 

 acceleration, as Packard says tbat there were only live pairs of abdominal t'eiit and tbat these were 

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

 constant difl'erenccs in development is a reason for regarding them as three distinct species, but, 

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

 existence of profound moditicatious in the life histories of adults which have reuuiiued almost 

 exactly alike. 



Careful and minute comparison between atlult specimeus from Beaufort and Nassau showed 

 the closest agreement in nearly all particulars (v. Cliai>. v, I't. First, Section ii), and it has there- 

 fore seemed best for us to regard them as belonging to 4 single species; the more so since our 

 discovery that diflerent individuals of another species found at Nassau {Alpheun Hmdcyi) difler from 

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

 heterochelis dit!er from the Bahama specimens. 



Alpheun minor and Alpheus heterochelis are very distiuct species. The adults have diverged 

 from one another so far that one coulil 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 remaiued almost absolutely 

 uuchauged, except as regards the reproductive elements and their product. 



Section V. — Larval development op Alpheus saulcyi. 



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

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

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

 overlaps the head. 



First larra (length,^ i^^o 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.l, C, 7,!), and PI. xxii. Figs. 1-8, 12. In both varieties the animal hatched as a scliizo- 

 pod, loosely infolded in a larval skin, but not invariablj', as I have noticed that in one or two caseH, 

 where females of the longicarpus with very few, perhaps half a dozen eggs, produced young, th6 

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

 tained after the second molt and 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 telson, and appendages. Kudimentary gills are present and a remnailt 

 of unab.sorbed green yolk is conspicuous in the stomach. The carai)ace 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 ocidar spines 

 (PI. XXII, Fig. G), 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 carai)ace. A 

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



Both pairs of antenn<e are biramous and jointed. The auteuuules (Fig. 8) ccmsist of a stout 

 peduncle, a short endopodite, 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 antenuic 

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

 two joints, bearing a rudimentary flagellum, 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) are deeply cleft, as in the adult. 

 The outer branch is dentated at its distal end and carries a pali)us. The first maxiihe (Fig. G, 



