288 ZOOLOGY. 



workers being sexually immature. In the ants, still further 

 division of labor occurs among the workers. Some individuals 

 act as soldiers for the protection of the ordinary workers. 

 Some species of ants make slaves of other species of ants 

 which do the work of the colony, or of other animals (aphides) 

 for the purpose of feeding on their secretions. A high order 

 of intelligence and skill is shown by certain members of this 

 group, the highest, apparently, shown by any of the inverte- 

 brate animals. 



326. Library Exercises. Reports on the social life of bees and ants; 

 on the animals captured and utilized by ants ; on power of flight in ants ; 

 on queens among ants and bees ; on myrmecophilous (ant-loving) insects ; 

 on intelligence among insects and spiders. 



327. Classification. 



Class I. Crustacea (Crayfish, Crabs, Barnacles, etc.). Arthropoda, 

 chiefly inhabiting the water and breathing by means of gills or through 

 the body wall. The head typically consists of five segments more or less 

 fused and bearing two pairs of antennae or feelers, one pair of mandibles, 

 and two pairs of maxillae. The thorax or second region of the body may 

 be separate from or fused with the head (cephalothorax}. It possesses a 

 variable number of segments, which usually bear the locomotor append- 

 ages. The remainder of the body (abdominal segments) is normally of 

 distinct segments in which the appendages are much reduced. The chitin- 

 ous skeleton is ordinarily well developed. 



Subclass i. Entomostraca. Crustacea, small and simple in organization, 

 with a variable number of segments of which the appendages are simple 

 and less diverse than in the next subclass. Many of them are parasitic 

 and degenerate. A metamorphosis occurs. The" group embraces many 

 small free forms, found both in fresh and salt water, some fish parasites, 

 and the sedentary barnacles. Here belong Cyclops and Daphnia, which 

 occur abundantly in fresh-water pools and feed on the algae common 

 there. They constitute an important portion of the food of the fresh- 

 water fishes. They multiply very rapidly and keep closely up to the limit 

 of the food supply. The eggs of many of them can resist drying to a 

 remarkable degree. This is of manifest importance when we remember 

 that they frequent pools in which drouth is not uncommon. 



The barnacles (Cirripedia) are Crustacea which in adult life become 

 attached to the rocks near low water-mark or to floating objects of 

 various kinds. The bottoms of ships become foul with them. The group 

 is especially interesting in that it points to the giving up of free motion, 

 which its ancestors possessed, for a mode of life wholly different, and 

 demanding marked changes of structure. They possess, besides the 



