LIFE AND THE CELL 53 



SO much apparatus is devoted to digestion and absorption, still more ap- 

 paratus is required in order that the parts can carry on their work. We have 

 muscle fibers in the walls of the alimentary canal which in the esophagus 

 aid in swallowing, and in the stomach bring about the churning motions 

 that facilitate the chemical part of the digestive process, while in the in- 

 testine they effect the discharge of food along its course. All these parts are 

 equipped with blood vessels which supply oxygen, remove waste and carry 

 away absorbed food materials to be distributed to other parts of the body. 

 And, again, the movements of the muscular coats of the alimentary canal, 

 the secretions of glands and the regulation of the blood supply are co- 

 ordinated through the agency of the nervous system and also by special 

 kinds of hormones or internal secretions. These agencies are required to 

 make it possible for the parts more immediately concerned in digestion 

 and absorption to function in an adequate manner. 



But in addition to the organs that are directly accessory to the digestive 

 apparatus, animals are equipped with tentacles, teeth and various other 

 organs for the capture of prey. The sharp claws of the cat, the poison 

 glands of the spider and the tentacles of the octopus are all devices to en- 

 able their possessor to capture prey upon which the digestive juices of these 

 animals may act. But further complications arise by the development of 

 organs and instincts subsidiary to these activities of capturing and over- 

 coming prey. A striking instance is furnished by the common orb-weaving 

 spiders. Toward evening in summer time one may often witness the mar- 

 velous performance of spinning an orb web. The making of the frame of 

 the orb, the placing of the rays, the spinning of the spiral of sticky web 

 and the formation of the central disc, or hub, are carried out with a nicety 

 and precision that have excited the admiration of all observers. The web 

 finished, the spider takes up its position head downward in the center, with 

 its feet on the rays where they readily feel the agitation conveyed by the 

 struggles of an entangled insect. Following the signal, the spider rushes out 

 upon its prey, often employing more web in the endeavor to impede the 

 movements of its victim. Then comes the sudden rush, the burial of the 

 fangs and afterward the leisurely meal. Here we have a complex series of 

 acts in preparation for capturing prey, which in turn is a preparation to the 

 acts of overcoming and feeding upon it, and these activities in turn are 

 more directly subservient to the various acts involved in digesting and 

 absorbing food. 



We might take another illustration from the industry of the hive bees, 

 among which there is not only food collecting, but food storing, and, in 

 preparation for food storing, the construction of the beautifully regular 

 six-sided cells of the honeycomb. Or, again, we might cite the grain gather- 

 ing and storing of the agricultural ants and the peculiar fungus-growing 

 industry of certain species of ants and termites. These activities, indirectly 

 accessory to nutrition, often involve the evolution of highly specialized 



