NO. 2 RECOGNITION AMONG INSECTS McINDOO 43 



dectiilarius, comes from three invaginated sacs. These sacs He just 

 beneath the first three abdominal terga. Each opens to the exterior 

 in the articular membrane by a pair of round apertures, one of which 

 lies near and on either side of the median line. Gissler ( 1890) figures 

 the scent^producing organ of the nymph of the common pine aphid, 

 Lachnus strobi. Here an external opening of the gland lies on either 

 side of the fifth abdominal tergum. 



Mayer (1874) found a quite complicated scent organ in Pyrrho- 

 coris apterns. Close to the median line of the metathoracic sternum, 

 a slit opens into a saclike cavity. Midway between the two ends of 

 this cavity a flask-shaped vessel, the reservoir, leads off at right 

 angles. The kidney-shaped gland lies between the reservoir and the 

 integument ; the collecting tube, whose free end is dichotomously 

 forked, passes lengthwise through the center of the gland and unites 

 with the neck of the flask-shaped reservoir. The walls of the gland 

 are composed of oblong secreting cells. In the inner end of each cell 

 a secreting tubule arises flasklike and runs into the collecting tube. 

 The secretion is stored in the reservoir, and except when the insect 

 is irritated is prevented from escaping into the saclike cavity by a 

 valvelike apparatus. A sweet odor similar to that from chloroform 

 is emitted from this organ. 



(c) GLANDS IN THORAX OF BEETLES 



Lacordaire (1838) reports that D ytiscus 2ind Gyriims, when picked 

 up, emit through the articulations between the head and prothorax, 

 between the latter and the mesothorax and between the metathorax 

 and abdomen a milky and fetid liquid. 



Plateau (1876) noticed that Dytiscus and Aciliiis emit, sometimes 

 at the same moment, two different kinds of liquids. The one having 

 a milky appearance issues from between the head and the tergite of 

 the prothorax, the other is yellowish and exudes from between the 

 meso- and metathorax. At each place where the liquid is emitted the 

 secretory organ is composed of many unicellular glands which lie 

 just beneath the hypodermis. The milky liquid is not venomous and 

 thus can not be used in the capture of prey, and also it probably 

 does not aid the sexes to find each other, because it does not have 

 a pronounced odor. It can not be a means of defense because it is 

 neither acid, nor strongly odorous and the quantity secreted is entirely 

 too small for this purpose. The yellowish liquid perhaps forms an 

 attractive coat on the surface of the bodv. 



