LARVAE. 



451 



of the ganglionic chain, and in the later members of the series 

 by reduction of the abdomen as an organ of locomotion. 



1 The Caridid zoaea is somewhat more advanced than the typical form, 

 having three pairs of maxillipeds, and a fan-shaped telson, replacing a caudal 

 fork. In Palaemon, Crangon, and Palaemonetes vulgaris rudiments of the 4th 

 and 5th (in the Palaemon of the 6th) thoracic limbs are also present. 



! The mysis stage in its highly modified Phyllosoma form. 



3 With rudiments of thoracic limbs 3-7. 



1 The 3rd maxillipeds rudimentary. 



5 The trunk and abdominal limbs are present, but uniramous. 



In Penaeus the young hatch out as nauplius larvae, but in the 

 great majority of the Decapods, although a well marked nauplius 

 stage, followed by the shedding of a larval cuticle, is passed 

 through in the egg (cf. Fig. 282), larval life begins at a later 

 stage. As will be evident from inspection of the table, the stage 

 at which the larva is hatched becomes, on the whole, more and 

 more advanced, the higher the degree of differentiation of the 

 adult form. In other words there is a tendency to the sup- 

 pression of the earlier stages of the life-history, as later stages 

 are added. The mysis larva is at the end of the metamorphosis 

 of Penaeus, while it initiates that of the lobster. 



The occurrence of the mysis stage in the development of many 

 groups of Decapods in which the larva resembles, in several 

 particulars, the least differentiated members of the series, and 

 still more the Schizopods with one group of which, the 

 Euphausiidae, the Penaeidea are closely allied is a pheno- 



