3 28 



7 HE CRUSTACEA 



losing its spines, and the appendages gradually assuming their 

 definitive characters. The development of the antennae appears 

 to be peculiar in that the endopodite develops as a lateral branch, 

 the distal portion of the larval append- 

 age becoming the large exopod. 



In a second series of larval forms of 

 the Erickthus-type (Fig. 193), belonging 

 to the genera Psenderichthus, Gonerichthiis, 

 etc. (Pseudosquilla and Gonodadylus), the 

 youngest stage known possesses already 

 four or five pairs of pleopods, and the 

 last six thoracic somites are without any 

 trace of appendages. 



The larvae of the Alima-type (Fig. 

 194), belonging to the genus Squilla, are 

 known to leave the egg at a stage cor- 

 responding with that last described. 

 They are distinguished from all the pre- 

 ceding forms by the generally more 

 slender body and short and broad cara- 

 pace, and more constantly by differences 

 in the armature of the telson and raptorial 

 limbs. 



Lister has described a very remark- 

 able larva, which appears to correspond 

 to a metanauplius- stage. The form of 

 the carapace makes it very probable that 

 it belongs to the Stomatopoda, and, if 

 so, it shows that some members of the 

 order leave the egg at a much earlier 

 stage than has hitherto been supposed. 



The great size attained by some of 

 these larvae, especially by those of the 

 Alima-type, which may exceed two and 

 a half inches in length, has given rise to 

 Later larva of the first Bruit- t h e suggestion that they are abnormally 



thus-type, a , antennule ; a , an- J . . J 



tenna;ai-a5, pleopods; a, uropods; hvpertrophied forms which, by being 

 Ir, rudiments of gills ; I-VIII, tho- J r , 



racic appendages. (After ciaus, swept out to sea, have been prevented 

 from completing their metamorphosis. 

 As in the similar cases of the Phyllo- 

 soma-larvae among Decapods and the Leptocephahis -larvae of eels, 

 however, there appear to be no grounds for accepting this view, 

 and it is definitely rejected by Hansen as a result of his extensive 

 studies on the group. 



The metamorphosis of the Stomatopoda is of great importance 

 in helping to interpret the larval forms of the Decapoda. While 



FIG. 192. 



