APPENDIX B 



655 



bees and a few other insects (Strepsiptera) ; and the horntails, saw-flies, ichneumon 

 flies, gall wasps, chalcid egg parasites, ants, velvet ants, wasps, and bees 

 (Hymenoptera) . 



Phylum XII. CHORDATA (cor da' ta; Greek, chorde, "cord," i.e., the 

 notochord). 



The backboned animals and their allies. The vertebrates constitute 

 the majority of the chordates and include man and all his nearest rela- 



Fig. B.25. Representative higher insects. Upper: left, the Colorado potato beetle, Coleop- 

 tera; center, a large African scarab beetle, Coleoptera; right, the plum curculio, a snout 

 beetle, Coleoptera. Lower: left, the house fly, Diptera; right, a mud dauber wasp, Hymenop- 

 tera. (Courtesy Ward's Natural Science Establishment, Inc.) 



tives. The chordates are the most highly developed of all animals. Among 

 their general characteristics are the following: 



Triploblastic. Bilateral symmetry. Metamerism evident. Coelom 

 present; organ systems highly developed. Endoskeleton always present 

 at some stage. Its characteristic form is the notochord, a longitudinal 

 dorsal rod, replaced to varying degrees in higher forms by the centra 

 of a series of vertebrae, which together constitute a vertebral column 

 (backbone). Respiration always involving the pharynx; gill clefts or 

 pouches present in this region at some stage of development (these per- 

 sistent as functional gill clefts only in the classes below Amphibia). 

 Central nervous system composed of a dorsal hollow nerve cord, the 

 anterior portion of which forms the brain in the vertebrates. 



