HIGH SCHOOL ZOOLOGY. 200 



acles are also very directly related to a series of large aii'-sacs, 

 which buoy up the locusts in their flight. 



25. There is a conspicuous difference between the end of the 

 abdomen in male and female specimens ^ in the latter (Fig. 141) 

 the ovipositor serves to drill the holes in the ground in which the 

 eggs are laid, surrounded by a stiff secretion furnished by S[)ecial 

 glands. Oviposition occurs in the fall, and development begins 

 at once, but is checked by winter, so that the young larvse only 

 escape from the eggs in the spring. Apart from the circum- 

 stance that they are destitute of wings, they resemble the parent 

 in form ; the complete resemblance is attained during a series 

 of moults, after each of which the body becomes larger and the 

 rudimentary wings more evident. No complete resting-stage 

 occurs such as the "chrysalis" of the buttei-fly, but the insect is 

 said to be in the " pupa" stage, before the last moult, which con- 

 vei'ts it into the adult (imago) stage : the locust and its allies 

 are consequently said to develop without metamorphosis. 



26. According to a recent computation, the number of species 

 of living animals described, amounts to some 272,000 ; of these, 

 200,000 belong to the class of the Insecta, and are consequently 

 constructed upon substantially tlie same plan as the locust 

 described above. Although only some 6,000 of these occur in 

 Canada, yet there is such a wealth of form, and such differences 

 of habit within the limits of this single class, that it will be 

 impossible to do more here than indicate the chief modifications 

 of the insect type, which characterize the various orders. 



Most of these are more specialised than the type described, 

 so it may be as well to glance in the first place at the more 

 primitive forms. Such, like the cockroaches (Blattidce), and 

 earwigs (Forjlculidce), are to be found within the order 

 (Orthoptera) and sub-order to which Caloptenus belongs. The 

 order receives its name fi-om the position which the wings 

 assume in rest in the family (^Acrydidce), in which it is 



