38 INSECTS 



they are of little use. Their habits in the early stages 

 are about as unlike those of the adults as it is easily 

 possible to imagine. The larvae live in all sorts of semi- 

 liquid excrementitious matter and are known as rat- 

 tailed maggots, because of the long anal process by 

 means of which they obtain air from above the surface 

 of the filthy mess in which they live. 



The number of flies known to us is already very 

 great, and the number that still remains to be studied 

 is probably even greater; while as to their habits we 

 know them in the most general way only. There may, 

 therefore, be groups more decidedly beneficial to 

 plants than anything that I have mentioned; but 

 there can be nothing comparable with the bees, since 

 none of the flies store food for their progeny. 



The fact is, then, that many plants depend for their 

 reproduction entirely upon insect visitors. Some flowers 

 are so constructed that only very specialized forms can 

 accomplish the function of pollination and there is in 

 many such cases a mutual dependence: the insect can- 

 not exist without the plant nor can the plant continue 

 its kind without the insect. Other flowers issue a general 

 invitation by bright colors, wide open parts, abundant 

 pollen or filled nectaries, readily accessible to anything 

 that may come along. Yet others depend upon nectaries 

 that are attractive, but are so situated that any insect 

 that succeeds in gaining access to them must of necessity 

 pay in pollenizing. And here we come to a subject on 

 which the botanist has his say, and shows how ingenious 

 are some of these plant structures and how well adapted 

 to their end, so that pollination may even be accom- 

 plished without the necessity for bringing the pollen 

 into contact with the insect at all, the latter merely 

 releasing the trigger that restrains the distribution of 

 the fructifying material. 



