448 



CRUSTACEA MALACOSTBACA. 



FIG. 282. Embryo of Astacus fluviatilis in the nauplius 

 stage. A (above) rudiment of eye ; a', a" first and second 

 antenna ; G cerebral ganglion ; ga% ganglion of the second 

 antenna ; gm ganglion of the mandible ; I upper lip ; 

 m mandible ; TA thoraco-abdominal rudiment ; A (lying 

 in TA) anus (from Lang, after Reichenbach). 



Isopoda) a well- 

 marked stage with 

 two pairs of an- 

 tennae and man- 

 dibles, followed by 

 the shedding of a 

 larval cuticle, has 

 been recognized in 

 the development of 

 the egg as corre- 

 sponding to the 

 nauplius larva of 

 other Crustacea. 

 (Compare the cor- 

 responding stage in 

 the development of 

 the fresh -water 

 crayfish, Fig. 282.) 

 In the remaining 

 Malacostraca, i.e., 

 in the Euphausiid 



Schizopods, in Stomatopods and Decapods (for the development 

 of the Syncarida see p. 462) a metamorphosis presenting varying 

 degrees of completeness is nearly always found in the life- history. 

 Compared with the gradual series of stages which in the 

 Phyllopod Branchiopods and most Copepods leads from the 

 nauplius larva to the adult condition, the metamorphosis of 

 the Malacostraca is 

 characterized by some- 

 what abrupt transi- 

 tions from one larval 

 stage to another, and 

 by the introduction of 

 stages which are not 

 in the direct line lead- 

 ing to the adult form. 

 " The metamorphosis 

 of the lower Crustacea Flo 283 _ Crab zoaea (TMa)> after the flrst moult . ^ A 



tVmj K^ar tViA amp first and second antennae ;/', Kf", the two pairs of 



biramous appendages corresponding to the first and 



relationship to that of b e a c c k n ?frSm r ciau s r xil1iPedS : ZS ^^ ^ ' 



A 



