i6o 



CRUSTACEA EUCARIDA DECAPODA 



behind is converted into the Protozoaea (Fig. 107), possessing two 

 pairs of biramous inaxillipedes. It should be noted that the 

 maxillae, which are foliaceous in the adult, are laid down in this 



A' 



FIG. 107. Protozaea larva of Peneus, sp. x 25. 

 (From Balibur, after F. Miiller.) 



condition in the larva, and this prin- 



ciple holds good throughout Crus- 



tacean metamorphosis, viz. that when 



a limb is foliaceous in the adult it 



is foliaceous in the larva, and when 



biramous in the adult it is biramous in the larva. Whilst the 



rest of the thoracic limbs are still rudimentary, the sixth pair of 



pleopods are being precociously developed (Fig. 108), being the 



only precociously formed limbs in the Peneidea, though the abdo- 



minal segments are fully marked off before the thoracic segments, 



and so must be considered as precocious in development. When 



antennae ; Ab.fJ, 6th abdominal 

 appendage ; Mxp, 2nd maxilli- 

 pede ; T, 4th-8th thoracic append- 

 ages (future walking legs). (After 

 F. Miiller.) 



