XIV 



INTBODTTCTION. 



is the large branchial region, which may be divided into anterior, 

 epibranchial (br 1 ) ; middle, mesobranchial (br 1 ) ; and posterior, 

 metabranchial (br n ) lobes. 



On the under surface of the carapace on either side of the 

 mouth a curved line divides off an anterior, subhepatic (Fig. iii., sh) 

 from a posterior and internal pterygostomial or anterior pleural 

 region (pt). 



The appendages of the thoracic region in the Crab correspond 

 closely to those of the Prawn. The posterior five are the 

 ambulatory legs, the first of which is developed into the great 

 pincer-claws or chelce, while the rest are simple. The third pair of 

 maxillipedes (Fig. iii., e) differ very much in shape from those of the 

 Prawn, their ischiopodite and meropodite being greatly expanded, 

 and the two appendages being applied closely to one another by 



.r"; 





Fig. III. Oral region of a Crab. 



a,Eyes; b, antennules ; c, third joint of antennas ; c', first joint of an tenure; 

 c", second joint; d, epistome ; e, external maxillipedes; sh, subhepatic 

 region ; pt, pterygostomial region. 



their inner edges, so as to form a sort of pair of folding-doors 

 closing up the orifice of the mouth. The remainder of the oral 

 appendages (Fig. iv.) with differences in detail, resemble the 

 corresponding structures in the Prawn in their general arrange- 

 ment. The external antennae (Fig. iii., a) are very small, and their 

 basal joint or coxicerite is fused with the antennary sternum or 

 epistome, so that what is frequently called the basal joint in 

 descriptive carcinology is really the basicerite , the lateral squame 



