468 



CBTJSTACEA. 



of slits is present. The facetted eyes are of considerable size, but 

 are not stalked. Between the facetted eyes there is in addition an 

 unpaired simple eye, the Entomostracan eye. The Zowa larvae of the 

 short-tailed Decapoda (Crabs) are, as a rule, armed with spinous 

 processes. They usually have one frontal spine, a long, curved dorsal 

 spine, and two lateral spinous processes of the cephalo-thoracic shield. 

 The Zoa, however, is not by any means always the earliest larval 

 stage. Passing over those cases in which the larva has the Zo?ea 

 form but is without the middle maxillipeds, there are Podophthal- 

 mata (Penceus), which leave the egg as Nauplii (fig. 367). Thus 



FIG. 368.- Zocea of Inachug in advanced stage with rudiments of the third niaxilliped (ff") 

 and the five pairs of ambulatory feet (5Sp) ; C, heart ; L, liver, b, Megalopa. stage of 

 Port units; Ab, abdomen. F' to ,F V first to fifth ambulatory legs. 



the developmental history proves that the series of forms of Ento- 

 mostraca and Malacostraca are continuous. 



During the growth of the Zoa?a, the subsequent metamorphosis of 

 which is quite gradual and always different, the six (five) pairs of 

 thoracic legs, which are as yet absent, sproiit out beneath the 

 cephalo-thoracic shield. The abdominal feet also make their appear- 

 ance on the abdomen, and the larvae finally enter the Schizopod-like 

 stage, from which the adult form proceeds. The Crab Zocea, how- 

 ever, after a later ecdysis, enters upon a new larval stage, that of the 

 Megalopa (fig. 368, 6) ; in this stage it already presents the cha- 

 racters of the Brachyura, but still possesses a large abdomen, which 

 is indeed ventrally flexed, but provided with a caudal fin. 



