. Elementary biology; an introduction to the science of life. Biology. 374 ELEMENTARY BIOLOGY. is illustrated by the skunk. This animal, as everyone knows, is capable of ejecting a foul-smelling liquid from a gland at the rear of the body when it is greatly agitated. Real fighting appears among animals that have mouths and appendages that are capable of grasping. These organs are at the same time food- getting organs. Lob- sters and crabs are very pugnacious ani- mals, or at least that is the impression they make upon the ob- server. Most of the mollusca (clams, oys- ters, scallops, etc.) de-
. Elementary biology; an introduction to the science of life. Biology. 374 ELEMENTARY BIOLOGY. is illustrated by the skunk. This animal, as everyone knows, is capable of ejecting a foul-smelling liquid from a gland at the rear of the body when it is greatly agitated. Real fighting appears among animals that have mouths and appendages that are capable of grasping. These organs are at the same time food- getting organs. Lob- sters and crabs are very pugnacious ani- mals, or at least that is the impression they make upon the ob- server. Most of the mollusca (clams, oys- ters, scallops, etc.) de- pend on their armors for defense against possible aggressors; some of them, how- ever, as the octopus, are very good fighters (Fig. 95)- Among the insects many are predatory, using their append- ages (Fig. 191) or their mouths (Fig. 192) in catching prey. But very few use these organs in fighting their enemies. The colonial insects, especially the ants, furnish the best examples of this mode of protection (Fig. 193). The bees, wasps, and hornets fight when they are disturbed or when the colony is disturbed, but in fighting they use the sting (see Fig. 194), which has nothing to do with food-getting or with locomotion. The horns of mammals are associated with the instinct to defend or fight, and are quite independent of the organs or Fig. 195. The fall of a leaf A, leaf dropping off; s, self-healing scar remaining on twig; B, microscopic view of section through base of leafstalk; a, angle between base of stalk and twig. In plants that regularly drop their leaves in the autumn there is formed a special layer of cells in the stalk of each leaf, and sometimes of each leaflet of a compound leaf. These cells, s /, are thin-walled and turgid. Their contents break down into a mucilaginous mass, which dries up. A slight movement is now sufficient to break the fibrovascular bundle at this point, and as the leaf is removed the exposed surface becomes a self-healing scar. Please note that
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