CRUSTACEA. 



465 



has discovered that the larva leaves the winter eggs in the form of a 

 Nauplius (fig. 209). This Nauplius closely resembles that of the Phyllopods. 

 The body is elongated and in addition to normal Nauplius appendages 

 is marked by six pairs of ridges the indications of the future feet, _The 

 anterior antenna? are as usual small ; the second large and biramous, 

 but the masticatory bristle characteristic of the Phyllopods is not present. 

 The mandibles are without a cutting blade. A large upper lip and unpaired 

 eye are present. 



The adult form is attained in the same manner as amongst the Phyllo- 

 pods after the third moult. 



MALACOSTRACA. 



Owing to the size and importance of the various forms 

 included in the Malacostraca, greater attention has been paid to 

 their embryology than to that of any other division of the 

 Crustacea ; and the proper interpretation of their larval forms 

 involves some of the most interesting problems in the whole 

 range of Embryology. 



The majority of Malacostraca pass through a more or less 

 complicated metamorphosis, though in the Nebaliadae, the 

 Cumaceas, some of the Schizopoda, a few Decapoda (Astacus, 

 Gecarcinus, etc.), and in the Edriophthalmata, the larva on 

 leaving the egg has nearly the form of the adult. In contradis- 

 tinction to the lower groups of Crustacea the Nauplius form of 

 larva is rare, though it occurs in the case of one of the Schizopods 

 (Euphausia, fig. 212), in some of the lower forms of the Decapods 

 (Penaeus, fig. 214), and 

 perhaps also, though this 

 has not been made out, in 

 some of the Stomatopoda. 



In the majority of the 

 Decapoda the larva leaves 

 the egg in a form known 

 as the Zoaea (fig. 210). 

 This larval form is 

 characterised by the pre- 

 sence of a large cephalo- 

 thoracic shield usually FIG. 210. ZO^.AOFTHIAPOLITA. (After Claus.) 

 armed with lateral, an- ""*' second Pte- 



terior, and dorsal spines. The caudal segments are well de- 

 B. II. 30 



