43S ARTHROrODA 



55. The Xcitropti-ra have net-veined wings and a holomelabolous 

 development; the nioulh parts are modified. 



^0. The Colcoplfra are luting inseets with tire fore wings changed 

 to elvtra; they differ fronr the somewhat similar Orthoptera h}' the com- 

 plete metamorphosis. 



57. The S/rcpsiplcrj are parasitic forms allied to the Coleoptera. 



5S. The Hymcnoplcra ha\-e partly bitiirg, partly licking mouth 

 parts; membranous wings with few nervures and holometabolous 

 development. 



5Q. The Rlivnchold are hemimetabolous or ametabolous, with 

 piercing mouth parts; tJie bed bugs and the Pediculiria are parasitic. 



00. The Diplcrj are holometabolous, witli piercirtg mouth parts and 

 not more than one pair of wings. The larva' of the tEstrida- are parasitic. 



6t. The Aplianiplcra are holometabolous, wingless, parasitic, with 

 suckiirg mouth parts. 



62. The Lcp id opicra have the wings covered with scales; labium and 

 labrum rudimentary, the maxilkr altered to a sucking tube; die develop- 

 ment holometaliolous. 



63. The DiPLciPODA have a head with three pairs of appendages; 

 the trunk with doulile segments, each bearing two pairs of legs, the genital 

 opeirings anterior. 



64. The term Myriapoda is frequently used to include Chilopoda and 

 Diplopoda. 



PHYLUM Vni. CHORD.ATA. 



Within recent }ears it has been realized that a number of animals, 

 formerly distributed anrong various groups, possess structural features of 

 great importance wliich aUy them to the vertebrates ; but they lack the N'er- 

 tebrx and many other features characteristic of that group, so that the name 

 cannot lie exteirded to embrace them. Yet since all possess, as a temporary 

 or a permanent feature, a structure knowi\ as the chorda dorsalis or noto- 

 chord, the term Chordata has been adopted to urclude them. 'Yhe nolochord 

 is an elastic rod arising from the entoderm and coming to lie between the 

 digestive tract and the ner\'ous s^'stem (I'lg. 0). 



In all Chordates the airterior (pharyngeal) portion of the alimentary 

 canal develops several pairs of pockets wliich grow outwards and fuse 

 with the ectoderm. The fused portion then breaks through, and the 

 pockets become coirverted into c^iU slils (branchial cicfis), which, in the 

 lower forms, allow the passage of water over the gills which line them. 



The central nervous system lies on one side of the alimentary canal, 



