RESEARCH ON THE DIGESTIVE SYSTEM OF THE SCHIZOPODA 17 



5, the latéral paired plates of the anterior chamber. 



5, the latéral paired plates of the posterior chamber. 



5; the médian unpaired eminence of the posterior chamber. 



/ the intestine leading from the posterior chamber. 



gl the common canals of the digestive glands. 



B. Study of microscopic sections. 



Œsophagus. 



The entrance into the stomach cavity is a passage running in an 

 obliqué direction forwards. It is divided into two ragions, the mouth and 

 œsophagus. The mouth is slit-like in form situated on the ventral surface, 

 FiG. 3. The paired appendages (mandibule and maxillas) are inserted on 

 either side of the mouth, fig. 6, 7nx. 



The œsophagus is a short narrow tube opening into the ventral wall of 

 the stomach cavity. The direction in which it runs is shown in fig. 3, 

 which is a vertical section through the médian plane. 



The lumen of the œsophagus is not cylindrical. It contains four 

 ridges running throughout its length as seen in fig. 5. Thèse ridges are 

 covered with a strong chitinous cuticle. Very fine hairs are seen covering 

 the surface of the mouth and œsophagus, fig. 3. 



The œsophagus is provided with a séries of circular muscle fibres. 

 Other muscular Systems, of greater strength, connect it with the external 

 integument, fig. 5, md. 



Glandular masses are found lying close to the œsophagus of the same 

 nature as those described as salivary in the Edriophthalmia. In fig. 5 thèse 

 masses are shown. We shall return to them again in the histological part. 



• Stomach. 



Almost ail the authors subdivide the stomach of the Crustacea into two 

 portions : the cardiac or anterior cavity in the ventral surface of which the 

 œsophagus opens, and the pyloric or posterior cavity. 



Différent functions are attributed to the cardiac chamber. On account 

 of the complicated chitinous plates that it contains armed with teeth, hairs, 

 spines or hooks, it is generally considered to hâve the rôle of masticating 

 and preparing the ingested food before it undergoes the action of the 

 sécrétions from the digestive glands-. 



