368 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



shown with more detail in Fig. 3, PI. XXII) have adult characters. They are biramous. 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 7iiaxill;e (Fig. 6, PL xxi) the scaphoguatliite 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 

 (eudopodite) has the adult form, while the innermost lobes of the adult appeudage (PI. xxiv. Fig. 

 9) are unrepresented. 



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

 ming organs. The endopodite of the lirst pair is short and stout and divided at its tip. That of 

 the third pair is three-jointed and equal in length to the exopodite. In the first pair of thoracic 

 legs (PI. xxi, Figs. 4 and 1) the inequality of the cliche is very marked, and, as we have already 

 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 are tipped with rudimentary in vagina ted hairs. The second pair of 

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

 third pair of pereiopods (Fig. -') end in bideutated 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 until after the lirst moult. The first pair (L'l. xxn, 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 (I'l. xxn, Fig. 1) and three succeeding pairs of pleopods have a 

 stout base, an outer blade like that of the first pair, and a shorter endopodite which bears on its 

 inner margin a lobule or palp. The sixth pair, or uropods (I'l. x\i, Fig. !>), are not yet free. The 

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

 nates the body, covering the outer uropodal limits, is a r ided, spatula te pi ale, with a median notch. 



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

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



Sci-ainl larva (length, ,',," inch). The lirst moult takes place either immediately or very soon 

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

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

 the eyes. (2) Both divisions of the autennules are considerably extended. The llagella, of I he 

 antennae are from three to four times their former size and are articulated into twenty to thirty 

 rings, the scale sill I not passing the peduncle. ('.}) The thoracic appendages have more of the 

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

 podites of the lirst four pairs are functional, and the last pair has grown forward. (4) The 

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

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

 incompletely hooded. 



Third l/irni (length, about '; inch). The third 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 respects 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 prominent 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 fhigellum nearly equals the carapace in length. As in the adult, the large chehe are very 

 prominent. The exopodites of the thoracic appendages have dwindled to rudiments. The view 

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



