282 



CRUSTACEA. 



limbs, and in a transformation of those already present. The first 

 antenna becomes jointed and develops the rudiment of the accessory 

 flagellum (Fig. 131), as well as the olfactory filaments of the prin- 

 cipal flagellum and the auditory organ in the basal joint. The 

 second antenna also (Fig. 131) becomes jointed, and, in the Phyllo- 

 so7na of Scijllarus, already shows indications of the lamellate shape 

 typical of the adult. In the mandible, a palp, at first simple and 

 later three-jointed, develops. The maxillae approach the adult form. 

 The first ma.Killipede and the fourth and fifth ambulatory limbs 

 now develop, while the penultimate ambulatory limb, as well as the 



second maxilli- 

 pede, develop still 

 further. From the 

 basal joints of the 

 maxillipedes and 

 ambulatory limbs, 

 the branchial 

 rudiments now 

 grow out. The 

 abdomen becomes 

 distinctly seg- 

 mented, and six 

 pairs of rudiments 

 of pleopoda appear 

 on it, the last pair 

 participating in 

 the formation of 

 the caudal fin. 

 Internally, the formation of diverticula leads to the development of 

 the hepatic tubes {!). This, in the Phyllosoma of Scyllarus (Fig. 

 129), is commenced by the development of three pairs of caeca, the 

 middle pair soon showing secondary ramifications. The Phyllosoma 

 of Palinurus (Fig. 129), on the other hand, shows, from the very 

 beginning, richer ramification of the so-called hepatic tubes. The 

 organs of the circulatory system are already, as Gegenbaur has 

 proved, of the typical Decapodan character. There is a heart pro- 

 vided with three pairs of ostia, from which the arterial vessels 

 proceed in a form characteristic of the Decapoda (Claus, No. 6). 

 The change of the Phyllosoma larva into the young stages of 

 the adult form, whicli are considerably smaller than the oldest 

 Phyllosoma, has not yet been directly observed. 



Fifi. 130. — Young Phyllosoma o{ Palinurus, shortly before hatchinc; 

 (after Claus, from Lang's Text-hook), oh, abdomen; L, liver; 

 II-III, second and third maxillipedes ; IV-VI, first three ambu- 

 latory limbs. 



