HARD PARTS OF THE COMMON CRAB. 171 



The hepatic lobes are bounded externally by the ser- 

 rated anterior margin of the carapace, posteriorly by the 

 cervical suture, and internally by the gastric area and 

 optic lobes. 



(c.) Posterior to the carapace, the dorsal or tergal sur- 

 face of the first abdominal ring or somite is visible in a 

 dorsal view. 



d. Make a sketch of the dorsal aspect, showing all these 

 points. 



II. The Ventral Surface. 



On the median line of the posterior portion of the ven- 

 tral surface, notice the abdomen (Fig. 91, ah), which is 

 bent downwards and forwards, so that its ventral surface 

 faces upwards, and is in contact with the ventral wall of 

 the thorax, while its dorsal surface faces downwards, and 

 is external. The abdomen fits into a groove or depression 

 in the ventral wall ov sternal plastron of the thorax, and 

 presents considerable sexual variation. 



a. In the male (Figs. 91 and 103, ab), it is naiTow 

 and wedge-shaped, and fits closely into its groove. Raise 

 it up with the handle of a scalpel, and notice the two 

 teeth by which it is locked into place. 



b. The abdomen of the" female (Fig. 102, ab), is 

 broad and rounded, and its inner or ventral surface is 

 concave, thus forming a broad chamber for containing and 

 protecting the developing eggs. It consists, in the female, 

 of six flattened, movable rings, or somites, which are cal- 

 cified and hard upon their exposed or dorsal surfaces, and 

 soft and membraneous on their internal or ventral surfaces. 



1. The first, second, third, and fourth abdominal somites 

 of the female carr>' paired appendages, the pleopods (Fig. 

 102,^?), Each appendage is fringed with long hail's, to 

 which, durincr the breedinoj season, the eorors are fastened, 

 and consists of : — 



