70 



The Form of Insects 



In these insects two glands are always present, an 

 acid and an alkaline; the former (fig. 51 p. g.) may 

 consist of a simple tube, of a bifid tube, of paired 

 tubes, or of a number of tubes ; the epithelial coat 

 of these is made up of several layers of cells. They 

 open into a large oval or spherical poison reservoir 

 (fig. S^ p, f) whence proceeds the duct to the sting. 

 The alkaline gland is a somewhat thick, irregular tube, 

 whose epithelial coat consists of a single layer of cells. 



Fig. 48. — Wax discs of Bees. a. Apis ' ' worker " \ b. Apis queen ; c. Melipona ; 

 d. Bombus. Magnified. From Riley, Insect Life, vol. 6 (U.S.Dept. Agr.). 



thrown into folds ; its duct opens alongside that from 

 the acid-gland reservoir. Ichneumon-flies and Sawflies 

 are provided with poison-glands like those of their rela- 

 tions the Bees and Wasps (43). Some Beetles eject 

 drops of blood from their leg-joints as a defence (2). 



Many insects form a waxy secretion for protection 

 or nest building. Beeswax is a well-known substance 

 used by the insects for making their comb ; it is 

 secreted by scale-shaped glands, formed of specially 



