to 



kind in pairs or in a number of pairs. The salivary glands 

 open into the mouth, and in addition to possessing the func- 

 tion of moistening foods, they are often developed for quite 

 different purposes. For instance, the silk glands of the silk- 

 worm and many other caterpillars, the poison glands of 

 mosquitoes and of certain Hemiptera are salivary glands, or 

 portions of the salivary glands specially developed for the 

 purpose. Other poison glands, scent glands, and glands for 

 many special purposes occur in insects, but quite apart from 

 the digestive system. The kidney tubes, or ' malpighian ' 

 tubes, of insects communicate with the food canal, at the 

 junction of the mid-gut with the hind-gut, that is where 

 the stomach and small intestine join. These are often very 

 numerous, and their function is excretory, similar to that of 

 the kidneys in other animals. The waste products are 

 passed into the intestine, and thence voided through the 

 anus with the undigested food and other waste matter. 



REPRODUCTION. 



Reproduction in insects is sexual, as a general rule, the 

 organs of the two sexes being borne in separate individuals. 

 Hermaphroditism (the two sexes in one individual) does not 

 occur normally, and it is not known that hermaphrodite 

 insects ever reproduce. The sexual organs are well devel- 

 oped, the testes of the male producing the spermatic fluid, 

 and the ovaries of the female, the eggs. In the female of 

 many species, the ovipositor is developed with special refer- 

 ence to the situation in which the eggs are to be laid. In 

 the case of many bees, wasps, and ants, the ovipositors are 

 often developed and vised as stings, and as such are well 

 known to most persons. Certain grasshoppers are able to 

 force the abdomen into the ground for the purpose of egg- 

 laying ; thrips, the cane fly and others have a saw-like 

 organ by means of which the eggs are deposited in incisions 

 in the surface of the plant tissue. 



Asexual reproduction occurs in plant lice, during 

 a portion of the year, and in a few other insects. This 

 parthenogenesis, as it is called, is a normal feature in the 

 life-cycle, and the offspring consists of females. The queen 

 of the honey-bee is able to lay, at will, fertilized eggs which 

 produce female, and unfertillized eggs which produce male, 

 forms. Another kind of asexual reproduction, known as 



