538 



ZOOLOGY 



The embryo is hatched in the form shown in Fig. 429, A. The 

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

 head-region ; an intermediate i:?'iMi7i;-rc^MM, the hinder part of which 

 already shows signs of segmentation (/- V) and a jDosterior bilobed 

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

 pair of small nnjointed appendages (1), each with two large setee 

 at its extremity : these become the antennules of the adalt. The 

 trunk region bears two pairs of appendages, the first of which (,:') 



Fir;, 429. — Three stages in the development of Apus. fs. frontal sensory organ ; L, digestive 

 gland; s. carapace; i—i, cephalic appendages; I— XlII, body-segments and appendages. 

 (From Lang's ComparoAU-c Anatomy.) 



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

 able for being hiramous or two-branched — being formed of a 

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

 cndopoditc ; and a large outer branch, the exopodite. This second 

 appendage becomes the antenna of the adult, and may be called 

 the antcnnary foot : it is the chief organ of locomotion of the 

 larva. The second-trunk appendage is the mandibular foot (J), so 

 called because it becomes converted into the mandible of the 

 adult : it is also biramous. The only internal structure to be 



