40 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 68 



A chitinous tube passing through the inner portion of the pore con- 

 nects the ampulla in the cell with the reservoir. The secretion is 

 easily seen on the surface of the chitin ; it has a bitter taste and emits 

 a repugnant odor. For more details concerning the secretion and 

 the structure of the gland cells see page 51. 



Under the foregoing heading may be mentioned the wax glands, 

 and the adhesive glands in the tarsi of various insects. While the 

 primary function of these glands is certainly to produce wax and to 

 enable insects to walk on smooth perpendicular surfaces, a secondary 

 use is probably that of recognition ; in regard to insects that fol- 

 low their trails, for example ants, the secondary use seems quite 

 plausible. For details concerning all these glands the reader is 

 referred to Dreyling's paper (1906) on the wax glands of bees; to 

 Packard (1903, p. 362) and others for information concerning the 

 wax glands of Aphididse and Coccidse ; to Packard (p. 1 11 ) , Schroder 

 (1912, pp. 10-13) and others for description of the unicellular glands 

 in the feet of various insects. 



2. CARUNCLES AS SCENT-PRODUCING ORGANS 

 (a) CARUNCLES OF A BEETLE 



Laboulbene (1858) describes some caruncular structures in 

 Malachhts bipustulatus as being two pairs .of beautifully red organs. 

 They are remarkably large, soft, eversible, Y-shaped and are thrust 

 out from the sides of the first and third thoracic segments. He was 

 unable to detect an odor emitted from a single insect, but when several 

 live insects had remained in a glass tube for a short time he detected 

 a slight odor. When irritated these beetles evert the caruncles and 

 direct them toward the enemy. He imagines that these organs emit 

 an insensible odor to us, but a perceptible one to their enemies and 

 that they are organs of defense. 



Liegel (1878) was the first to describe the anatomy of the car- 

 uncles of Malachius. He asserts that they are everted by blood pres- 

 sure and are retracted by muscles. Since he failed to find glands 

 in them, he refutes the view that Laboulbene advances, and he thinks 

 that they aid in respiration. 



(b) CARUNCLES OF A COCKROACH 



Gerstaecker (1861) describes a peculiar organ in the Indian cock- 

 roach, Corydia. This organ in both sexes consists of two pairs of 

 caruncular, evaginated saclike appendages which are located on the 

 pleura of the first and second abdominal segments. He thinks that 



