BRACHYURA. 293 



wanting. Claus, however, has described the presence of a long frontal spine 

 on the Zoaca of Maja. In a larva described by Dohrn (No. 121) as Fissocaris, 

 which has a long frontal spine and two pairs of large lateral spines, the dorsal 

 spine is wanting. In other cases the dorsal and lateral spines may be exceed- 

 ingly long, and may end in balloon-shaped swellings. Larvae thus provided 

 with latei-al spines projecting backwards were described as I'luteocariclae by 

 Clavs (No. S). a Zoaca form distinguished as Pterocaris is remarkable for 

 the wing -like elevations of the lateral parts of the carapace, and for the 

 transversely-broadened form resulting from this. 



Many of the Zoacac of the Brachyura are distinguished by the great develop- 

 ment of tlie spinous pirocess on the second antenna ; c.y., those of Xantlio 

 rivulosus (GouKi'.ET, No. 130) and of Panopcus Sayi (W. Faxon, No. 125), 

 in which this })rocess equals in length the long frontal spine. 



AViien the youngest Zoaca leaves the egg, it is not altogether free, but 

 appears surrounded by a somewhat loose and detached larval integument 

 (p. 119) ; this has been claimed by CoNX as the cuticle of the Protozoaea stage 

 jiassed through during embryonic life. Only after a moult, which usually 

 takes 2)lace early, does the Zoaca become free. A similar condition is found 

 in many other Decapoda (e.g., in all Anomura and many Macrura). F. Mijllek 

 (No. 16) has pointed out the morphological interest of a study of this larval 

 integument, the form of the tail in this youngest integument in AcUaeus, and 

 perhaps also in Maja, recalling that of the slirimp larvae. This larval cuticle 

 was utilised later by Paul Mayek (No. 137) in an attempt to derive the different 

 forms of telson and for phylogenetic purposes. More recently, further investi- 

 gations with regard to it have been made by W. Faxon (No. 125) and Conn 

 (Nos. 114 and 115). The spinous processes of the dorsal shield are alwaj's 

 wanting in the larval integument, but are often present as rudiments beneath 

 the cuticle, withdrawn in a telescopic manner. While, in the group of the 

 Gra})soidea [Sesarma), the larval integument, apart from the spinous processes, 

 is a fairly true cast of the Zoaca which proceeds from it, in most other 

 Brachyura it shows no inconsiderable deviations from that form. The antennae, 

 especially, appear in the larval integument in a higher degree of development. 

 The first antenna consists of a protopodite and two terminal branches provided 

 with setae, one of which is of considerable length. The second antenna is 

 specially remarkable for the presence of laige jirocesses provided with setae 

 on the exopodite. In the jiosterior region of the body, the caudal fork is usually 

 characterised by possessing seven feathered setae on each side. The number 

 seven seems to be typical in the setae of the telson throughout the Decapoda, 

 and renders the study of the hatclied Zoaca before the casting of the larval 

 integument a valuable aid in tracing back the shajie of the telson, which often 

 varies in a later stage, to the fundamental form already described (Paul Mayer). 



The series of ontogenetic stages wliich follow after the Zoaea 

 have usually received the same name, but have been more suitably 

 called Metazoaeae by Claus (No. 7). They do not, in general shape 

 {cf. the somewhat younger stage, Fig. 138), entirely resemble the 

 Zoaea, but are distinguished by the greater development of the 

 limb-rudiments. In the first antenna (Fig. 137 A) there is now an 

 unjointed protopodite showing the rudiment of the auditory organ 

 as a vesicular swelling, and two rudiments of flagella, the inner still 



