INSECTS 



passengers on ships, they have spread to all countries 

 where ships have gone. 



Besides the household roaches, there are great numbers 

 of species that live out of doors, especially in warm and 

 tropical regions. Most of these are plain brown of various 

 shades, or blackish, but some are green, and a few are 

 spotted, banded, or striped. Different species vary much 

 in size, some of the largest reaching a length of four inches, 

 measured to the tips of the folded wings, while the smallest 

 are no longer than three thirty-seconds of an inch in 

 length. They nearly all have the familiar flattened form, 

 with the head bent down beneath the front part of the 

 body, and the long, slender antennae projecting forward. 

 Most species have wings which they keep closely folded 

 over the back. In the Oriental roach, the wings of the 

 female are very short (Fig. 49 D), a character which gives 

 them such a different appearance from the males (E) that 

 the two sexes were formerly supposed to be differen t species. 



The roach, of course, was not designed to be a household 

 insect, and it lived out of doors for ages before man con- 

 structed dwellings, but it happens that its instincts and its 

 form of body particularly adapt it to a life in houses. Its 

 keen sense, its agility, its nocturnal habits, its omnivorous 

 appetite, and its flattened shape are all qualities very 

 fitting for success as a domestic pest. 



Many kinds of roaches give birth to living young; but 

 most of our common species lay eggs, which they inclose in 

 hard-shelled capsules. The material of the capsule is a 

 tough but flexible substance resembling horn, and is pro- 

 duced as a secretion by a special gland in the body of the 

 female opening into the egg duct. The capsule is formed 

 in the egg duct, and the eggs are discharged into it while 

 the case is held in the orifice of the duct. When the re- 

 ceptacle is full its open edge is closed, and the eggs are thus 

 tightly sealed within it. The sealed border is finely 

 notched, and transverse impressions on the surface of the 

 capsule indicate the position of the eggs within it. 



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