86 



cephalic region, and is bounded in front by a fleshy lobe — ■ 

 the labrum (PI. Ill, figs. 18, 20, lab.) or anterior lip — 

 and behind by the metastoma {met.) or posterior lip. On 

 each side of the mouth are the mandibles. 



Both the labrum and metastoma have closely packed 

 glands which have the appearance and structure of the 

 " salivary glands " found in the walls of the oesophagus. 

 It is not inconceivable that they have the same function 

 as the oesophageal glands. The mandibles also have at 

 their base a mass of glands which are continuous with 

 those in the ventral portion of the oesophageal walls. 



In the oesophagus (PL V, fig. 35) the epidermal cells 

 [eh. ep.) are of great length. In a soft crab with a 

 carapace 25 mm. in width these cells are 90 /* in length 

 and only 3 n wide. On the outer side of the epidermis 

 is a thin chitmous layer about 8 /* in width. This consists 

 of two layers — a thin outer structureless layer, the cuticle, 

 and a broader inner layer showing evidences of longi- 

 tudinal striations. On the inner side of the epidermis is 

 a well-marked basement membrane. Below the basement 

 membrane is a layer of connective tissue (der.) about 370 n 

 in width. This is composed of a dense reticulate mass 

 formed of intercrossing connective tissue fibres. There 

 are also small connective tissue cells scattered about. 

 Embedded in the connective tissue are numerous glands 

 which may conceivably be salivary glands, but which I 

 designate the oesophageal glands (sal. g.). 



On the outer side of the connective tissue of the 

 oesophagus is a layer of circular muscles — the constrictors 

 of the oesophagus (c. oe.) — and passing through the 

 connective tissue and attached to the basement membrane 

 are numerous muscle bundles — the dilators of the 

 oesophagus (oe. I.). 



Each oesophageal gland is globular and consists of 



