ORGANS OF SECRETION. 585 



of the intestine, and sometimes develope a small vesicle, or 

 urinary bladder, as in ditiscus, destined to receive their 

 scanty secretion, which is found by analysis to contain urea, 

 or a suburate of potash and ammonia, as the renal secretion 

 of higher animals. Many coleopterous insects, especially 

 the carnivorous species, possess glandular tubuli which pour 

 a very acrid matter into the rectum, and in the hymenoptera 

 there is frequently a poison-gland developed in the last ab- 

 dominal segment, which sends its secretion through a perfor- 

 ated sting of great density and sharpness. The testes and 

 the ovaries themselves, though more subdivided and compli- 

 cated, present the same elongated follicular character of 

 glandular tubuli. There are often numerous tubuli in the 

 male, like vesiculae seminales, connected with the vasa 

 deferentia ; and in the female we often observe, in the course 

 of the oviduct, one or more glandular organs, apparently 

 destined to secrete a fluid. to envelope the ova, as they pass 

 through the trunk of the united oviducts. 



Many insects form a glutinous secretion from distinct 

 glands, as from the two long tortuous labial glands of the 

 silk-worm, which, after being thrown out from small aper- 

 tures, hardens into fine silken filaments, destined sometimes 

 to assist in their progressive motion, or to suspend their ova, 

 or to entangle their prey, or to envelope and protect their own 

 body while in the torpid pupa state. As in the lower classes 

 of animals, numerous species of insects, when excited or 

 alarmed, produce vivid flashes of light, which they are capable 

 of prolonging for some time. There are often cutaneous 

 follicles, which pour out on the surface, secretions possessing 

 every variety of odour, as a means of protection when irri- 

 tated; frequently the odorous glands contained within the 

 segments, near the anus, can be protruded from the body 

 and retracted at pleasure. Some insects have the odorous 

 follicles placed near the head, or on the back, or along the 

 articulations of the trunk and of the extremities. Glandular 

 follicles on the lower part of the abdomen of the bees, secrete 

 the wax in which they envelope their ova, and their honey 

 is elaborated in the digestive organs, from the juices they 

 have collected in sucking the flowers of plants. 



The chylopoietic glands are but imperfectly developed in 

 the carnivorous tribes of arachnida, where, however, we 



