92 PHYSIOLOGY OF THE INVERTEBRATA. 



physiology of the alimentary canal in the OrtlioptRTa, Zepi- 

 doptera, Hymenoptera, and the Araneina. 



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

 cockroach) is very highly developed. The salivary glands 

 (Fig. 25, a and h) 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, h). Accompanying 

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



^-«f^' 



„. . . •-...■ _ Acinui 



. Chitinous tn 



eal ducts c 'r*' ' « il~-» Nuclei 



■\->, id 



»™ ^ „-.-Wer). 



Opening. |^ 



Fig. 25.— (a and l>) Salivary Gland of Blatta. 



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 Proc. Boy. Soc. JEdinb., vol. 14, p. 234; and Chemical News, 

 vol. 52, p. 195. 



