LIGIA. 77 



invagination, and their anterior ends attached to the 

 hypodermis of the middle of the preceding segment. In 

 the lateral, and also the epimeral regions, the body cavity 

 is almost entirely filled up with the muscles moving the 

 appendages ; these muscles are attached to the dorsal 

 side of the animal in these regions (lev. m.). The 

 longitudinal muscles of the ventral side (v.Lm.) have 

 their attachments similar to those of the dorsal side. 

 The joints of the thoracic appendages, like the appendages 

 themselves, are provided with extensor and flexor muscles. 

 The mandibles are provided with a powerful set of 

 muscles, attached to the dorsal side. The proximal ends 

 of the remaining mouth appendages have thickened 

 skeletal rods, forming an internal framework, to which the 

 muscles moving them are attached. 



The Digestive System. 



The digestive system consists of the alimentary canal 

 and its glands — the salivary glands, and the hepato- 

 pancreas or digestive gland. 



The alimentary canal can be divided into four parts — 

 the oesophagus, the stomach, mid-gut and rectum. 



The oesophagus (PL II., fig. 15 oes.) opens by a slit-like 

 aperture surrounded by the mouth appendages. Its course 

 is almost vertical, and it opens into the anterior end of the 

 stomach on the ventral side. The oesophagus receives the 

 secretions of the salivary glands. 



The stomach forms an efficient mill for triturating 

 the miscellaneous substances upon which the animal feeds. 

 It lies in the cephalic and first thoracic segments. The 

 wall of the stomach, which is composed of columnar cells, 

 is lined with chitin, and is folded in a complicated 

 manner ; thus a number of chitinous lamellae are formed, 



