334 GENERAL BIOLOGY 



is of little importance compared to the millions of lives lost each year 

 by the working out of the self-same principle that makes men think only 

 of the dollar they receive to-day, rather than of the ten-times-that- 

 amount they may have to-morrow, if they will but lay the foundations 

 to-day. 



Every worker who dies of a disease which could have been pre- 

 vented, causes each and every one of us to do a portion of his work. 

 This means that we must actually pay the expenses of keeping up such 

 a one's family without anything being contributed on their part. 



There is thus an underlying unity among all human beings, in that, 

 whether we will or not, we are our brother's keeper. 



This .is again well illustrated by taking into consideration the fact 

 that your own home and property may be as clean as it is possible to 

 keep it, but your neighbor's is not. The flies which breed in his manure 

 pile, or in his garbage heap, will come into your home and deposit the 

 neighbor's filth on your food. That this deposit is no mere trifle is 

 shown by an enlarged sketch of the fly's proboscis (Fig. 216). 



EXTERNAL APPEARANCE 



The hard exoskeleton has already been mentioned as well as the seg- 

 mentation of the grasshopper's body. The segments in this animal are 

 unlike those of the earthworm in not being all alike. 



There is a head, thorax, and abdomen, to which various jointed ap- 

 pendages are attached, a pair to each segment, where any appendages 

 are found at all. 



The three pairs of legs formerly gave them the name of Hexapoda. 

 Two pairs of wings are usually found upon the dorsal side of the second 

 and third segments of the thorax, while the tiny outer openings of the 

 tracheae known as breathing pores, spiracles or stigmata are arranged 

 in pairs on each side of two thoracic segments and on all the abdominal 

 segments except the last two or three. 



Grasshoppers as well as crickets and cockroaches are members of 

 the order Orthoptera ( ). All of this group have 



mouth-parts (Fig. 217), or jaws formed for biting and gnawing as well 

 as two pairs of straight wings, the first pair thickened, the second pair 

 thin, and, when at rest, folded like a fan under the first pair. 



A pair of jointed antennae or feelers extend forward from the head, 

 while a pair of large compound eyes located on the dorsal epicranium 

 and three ocelli or simple eyes are readily observed. The mouth-parts 

 consist of the labrum or upper lips, being hinged to the clypeus 

 ( ), a pair of heavy strong mandibles and a first 



pair of maxillae with feelers or palps ( ) at the sides, 



while the second pair of maxillae are fused together to form the lower 

 lip, called the labium, and are attached to crescent-shaped genae 



