218 



INVERTEBRATA 



CHAP. 



the adult by a series of moults in which the diminished or vanished 

 appendages reappear in the form of grasping claws, and in which 

 the hindermost segments of the thorax develop their appendages 

 as long legs with the rudiments of exopodites. 



In the case of other Stomatopoda the embryo develops within the 

 egg until it has reached the Pseudozoaea stage ; it then emerges as 

 an Alima larva, which differs only in unimportant details from the 



Pseudozoaea. The 

 subsequent develop- 

 ment of the Pseudo- 

 zoaea is the same as 

 that of the larva. 



Now these life- 

 histories justify us in 

 regarding the Stom- 

 atopoda as derived 

 from Schizopod ances- 

 tors, in which the 

 anterior thoracic 

 appendages were 

 gradually converted 

 into grasping claws 

 whilst the swimming 

 function was thrown 

 on the abdominal 

 appendages ; just as 

 we believe that Deca- 

 poda are derived from 

 Schizopoda, in which 

 the posterior thoracic 

 segments were de- 

 veloped into ambula- 

 tory legs whilst the 

 swimming function is 

 equally relegated to 



the abdomen. The five pairs of grasping claws constitute, from the 

 point of view of heredity, a single organ which is reproduced in the 

 Pseudozoaea and Alima larvae as two large functional pairs only. 



The Sessile -eyed Decapoda, including Cumacea, Anisopoda, 

 Amphipoda, and Isopoda, and the division Mysidacea of Schizopoda, 

 which are all grouped by Caiman (1909) under the name Peracarida, 

 enter on their free life similar to their parents in all essential features ; 

 but the just-born young of all these groups agree in having the last 

 segment of the thorax and its appendages suppressed; another, if 

 less well-marked, example of the same rule as that exemplified by 

 the larvae of Stomatopoda. 



Amongst the Isopoda, however, there are a considerable number 

 of genera which have developed suctorial mouths by a union of upper 



ur 



FIG. 166. Two later larvae of Stomatopoda. (After Clans.) 



A, Pseudozoaea stage of Erichthus Edivartlsi, ventral view. 

 B, All ma larva of unknown stomatopod. (This larva has moulted 

 since birth.) In A, in.rp* and mxp r >, rudiments of fourth and fifth 

 maxillipedes. In B, M6' s , rudiments of last thoracic legs ; r, 

 rostrum. 



