92 PHYSIOLOGY OF THE INVERTEBRATA. 



physiology of the alimentary canal in the Orthoptcra, Zcjn- 

 doptcra, Hymcnoptera, and the Araneina, 



(a) The Orthoptera. — The alimentary canal of Blatta (the 

 cockroach) is very highly developed. The salivary glands 

 (Fig. 25, a and i) of the cockroach are situated on each side 

 of the oesophagus and crop, and extend posteriorly as far as 

 the abdomen. They are about one-third of an inch in 

 length, and composed of acini (Fig. 25, I)), Accompanying 

 the glands are two salivary receptacles, one on either side of 



Salivary gland. 

 Salivary receptacle. 



Salivary gland 

 (under high power). 



Opening. 

 Fig. 25.— (rt and b) Salivary Gland of Rlatta. 



the crop. A quantity of the secretion* was extracted by 

 crushing about sixty glands of cockroaches, which had been 

 recently killed. The secretion was alkaline to test-papers. 

 A portion of the secretion was added to a small quantity of 

 starch, which was converted into glucose in twelve minutes. 



* Griffiths, in Froc. Roy. ISoc, Edlnh., vol. 14, p. 234; and Chemical Ntics, 

 vol. 52, p. 195. 



