302 



THE CRUSTACEA 



(Fig. 179, A) possesses two pairs of maxillipeds, the third pair 

 (Fig. 179, C) being present as rudiments. The carapace has its 

 posterior border produced into two lateral spines (greatly elongated 

 in Porcellana, Fig. 180), and a long rostrum is present. In the 

 next succeeding stage, the Metazoea (Fig. 179, B), the third 

 maxilliped becomes biramous and natatory (a point of distinction 

 from the Brachyuran type), and the uniramous ambulatory limbs 

 and the pleopods are developed as rudiments. 



The Brachyura, as a rule, are stated to hatch in the Zoea-stage 

 (Fig. 181), but since rudiments of the posterior thoracic limbs are 



C 



FIG. 179. 



Larval stages of Eupagurus bernhardus (Paguridea). A, Zoea. B, Metazoea. C, rudiments 

 of third maxillipeds in Zoea-stage. D, caudal fan of Metazoea. a', antennule ; a", antenna; 

 a 5 , fifth pleopod ; 6 , uropod ; k, rudiments of gills ; mftanf", the three pairs of maxillipeds ; 

 ol, labrum ; p'-p'v, first four legs ; r, rostrum ; t, mandibularpalp. (After Sars, from Korschelt 

 and Heider's Embryology.)- , 



frequently present, it might be more correct to, call the larva a 

 Metazoea. Throughout the group a very characteristic form is 

 given to the Zoea by the development of long spines on the 

 carapace. As a rule, a rostrum, a median dorsal, and a pair of 

 lateral spines are present. Of these, the dorsal spine (d.s) is 

 the most constant ; great importance was formerly attached to 

 it as a characteristic of the Zoea-stage. In many Brachyura the 

 larva when hatched is enclosed in a cuticle which is moulted shortly 

 after hatching, and this cuticle in many cases presents characters 

 differing from those of the larva which escapes from it. In 



