328 GENERAL ZOOLOGY 



An animal must be able to meet the conditions of environment 

 at any given time and to meet new conditions when the environ- 

 ment changes. The alternative is extinction. Man is inde- 

 pendent of his environment only to the extent that he can control 

 it by profiting by experience, a faculty that has been slowly 

 acquired. Adaptations center about certain activities which are 

 common to all forms of animal life. These are: 



1. Preservation of self, which consists in gaining sustenance 

 from the environment and in the protection of self from destruc- 

 tive agents both animate and inanimate. 



2. Preservation of race, which depends on each kind of orga- 

 nism reproducing its own kind in sufficient numbers to assure the 

 continued existence of the race. 



The examples of adaption discussed in the following paragraphs 

 have been chosen largely because of their obviously adaptive 

 nature. They illustrate states of fitness of a structure or function 

 for the accomplishment of certain ends. All of them center in 

 the two main activities of animals: self-preservation and race 

 preservation. 



Weapons.— Structures, such as claws, teeth, horns, etc., are 

 familiar examples of weapons, some of which may be used in 

 capturing food. An unusual weapon of highly specialized type 

 is the sting of the honeybee, Apis mellifica. The sting, located 

 in the sting chamber at the tip of the abdomen, consists of right 

 and left basal arms which curve toward each other in the mid- 

 line and then continue as a pair of lancets or darts, each of which 

 is barbed near the end (Fig. 184). The sheath, lying above the 

 darts also consists of two arms, paralleling the course of the arms 

 of the darts. The two arms of the sheath meet in the mid-line 

 to form a median bulb, beyond which the sheath tapers to form 

 a slender shaft. The sheath is hollowed on the side next to the 

 darts, the channel between the sheath and the darts thus forming 

 a poison canal, which in the region of the bulb expands into a large 

 cavity. The darts can be moved separately or together along 

 the lateral edges of the sheath. A large poison sac opens into the 

 enlarged region of the sheath. Arising from the free end of the 

 sac is a narrow tubular gland, which consists of two highly coiled 

 branches. The liquid produced by this gland is principally formic 

 acid, and the gland is known as the acid gland. In addition 

 there is an alkaline gland opening into the base of the sac. The 



