368 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



shown with more detail in Fig. 3, Pi. xxii) have adult characters. They are bira:n<>ns. The endo- 

 podite is stout and toothed at its apex. The more slender outer division bears a short spine 

 near the distal end. In the second masill.e (Fis- ti, PI. xxi) the scaphoguathite or respiratory 

 plate is most prominent. This is now composed of an anterior portion, bordered with from six to 

 twelve long plumose hairs and a posterior, rudimentary, and hairless lobe. The inner division 

 (endopodite) has the adult form, while the innermost lobes of the adult appendage (PI. XXIV. Fig. 

 9) are unrepresented. 



The maxillipeds are all biramous appendages, and their exopodites are the principal swim- 

 ming organs. The endopodite of the first pair is short and stout and divided at its tii). That of 

 the third pair is three-jointed and equaj in length to the exoi>odite. In the first pair of thoracic 

 legs (PI. XXI, Figs. -1 and 7) the inecpiality of the chehe is very marked, and, as we have alrea'ly 

 seen, it is so for some time before hatching. Individuals differ somewhat in this respect. The 

 articulations of the carpus and meros are distinct. The exopodites of this and of the three suc- 

 ceeding pairs of thoracic limbs ai'e tii)ped witli rudimentary iiivaginated hairs. The second pair of 

 pereiopods (PI. xxii, Fig. 1) are chelate, but the articulations of the carpus are not distinct. The 

 third iiair of pereiopods (Fig. 2) end in 'bidentated dactyles and have short exopodites. The 

 fifth pair are without swimming organs. 



All the abdominal appendages are present and functional, excepting the sixth pair. They 

 have only very short hairs nntil after the tirst moult. The first pair (PI. xxii, Fig. 5) consist 

 of a larger outer and smaller inner blade. This endopodite remains rudimentary in the adult 

 male, but nearly equals the exopodite in length in the female, as will be seen by reference to PI. 

 XXIV, Figs. -1 and 5. This convenient sexual mark probably appears early, but can not be relied 

 upon at this stage. The second (PI. xxii, Fig. 4) and three succeeding pairs of pleopods have a 

 stout base, an t)uter blade like that of the first pair, and a shorter endoiwdite which bears on its 

 inner margin a lobule or palp. The sixth pair, or uropods (PI. xxi, Fig. 'J), are not yet free. Tiie 

 inner and smaller divisions point forward, meeting on the middle line. The telson, which termi- 

 nates the body, covering the outer uropodal limbs, is a rounded, spatulate plate, with a median UDtcii. 

 Its free posterior edge is fringed with seven pairs of plumose spines, the tirst or median pair being 

 rudimentary, and the next four succeeding pairs long and nearly etpial. 

 • Second larva (length, ^0% inch). — The first moult takes place either immediately or very soon 

 after hatching. The animal as it now appears is shown in PI. xxi. Fig. 2. The principal external 

 changes thus produced are the following: (1) The rostrum and ocular arciies extend farther over 

 the eyes. (2) Both divisions of the antennules are considerably extended. The fiagella of the 

 antenme are from three to four times tlieir former size and are articulated into twenty to thirty 

 rings, the scale still not jiassiug the peduncle. {■>) The thoracic api)endages have more of the 

 adult characteristics. The articulations of the carpus of the second pair are distinct. The exo- 

 podites of the first four pairs are functional, and the last i)air has grown forward. (4) The 

 pleopods presently acquire swimming hairs; the telson plate is free and the uropods are func- 

 tional for the tirst time. (5) The last thoracic segment is still uncovered and the eyes are 

 incompletely hooded. 



Tliird larva (length, about ^ inch). — The tliird larva as it appears after the second moult, 

 which takes place in twenty-five to thirty hours after hatching, is represented in PI. xxi. Fig. 

 8. It has now the general adult character, and can not be called a larva in the strict sense. At 

 even this early age the pugnacious instinct is strong, and although only about one-sixth of an 

 inch long, it snaps audibly the fingers of its large ''hand,'' which is carried extended forward. It 

 also swims on the bottom of the jar in all resi)ects like the adult. Only a few globules of yolk 

 remain in the stomach. The gills are now quite prominent. They are evidently functional to 

 some degree, and were so, possibly, at an earlier date. The yellow and red pigment cells have 

 nearly all disappeared or are temporarily withdrawn from view. 



A most jjrominent change at the second moult is the extension forward of the rostrum and 

 the ocular spines, which form a hood over each eye. The autennal peduncle surpasses the scale, 

 and its ttagellum nearly equals the carapace in length. As in the adult, the large chelie are very 

 l)roininent. The exopodites of the thoracic a[)pendages have dwindled to rudiments. The view 

 of the head of a four-days old Alpheus is shown in Fig. 3, PI. XXi. 



