496 



ZOOLOGY 



SECT, 



Development. The eggs are centrolecithal, i.e., have an 

 accumulation of yolk in the centre surrounded by a superficial 

 layer of protoplasm. The process of segmentation and the forma- 

 tion of the germ-layers, has not been observed. 



The embryo is hatched in the form shown in Fig. 395, A. The 

 body is oval, and is divisible into three regions a large anterior or 

 liea<l-i'< ijiaii ; an intermediate tmmJc-region, the hinder part of which 



Fie. 395. Three stages in the development of Apus. fs. frontal sensory organ ; L, digestive 

 Klaiid ; x. carapace ; 1k, cephalic appendages ; I XIII, body segments and appendages. 

 (From Lang's Compai-atirc Anatomy.) 



already shows signs of segmentation (/- V} and a posterior bilobed 

 a iil region. The head-region bears a single median eye, and a 

 pair of small unjointed appendages (!}, each with two large set-t- 

 at its extremity, which become the antennules of the adult. The 

 trunk-region bears two pairs of appendages, the first of which (2) 

 is very large and fringed with seta3, but is chiefly remark- 

 able for being liirin<,us or two-branched being formed of a 

 proximal portion or stem, the protopodite ; a small inner branch, the 

 endopodite ; and a large outer branch, the cxopoditc. This second 



