XVII. BRANCH XII. — CHORDATA (chord, cord) 



If we recall, thoughtfully, all the animals thus far studietl, 

 we shall find that they are conspicuous for the lack of one 

 thing. T'hat is, that they have no backbone or anj^thing to 

 take the place of a backlione; hence they ai-e called inverte- 

 brates (in, without; vertebra, joint). All tlie remaining 

 members of the animal kingdom are conspicuous from the 

 fact that they have a spinal cohunn or some structure that 

 takes the place of it at some period of tlieir life. Those 

 that possess a real ]_iack])one, as most fishes, all birds, and 

 mammals, are known as vertebra Ic^^. Some of the animals 

 with which we arc yet to ljec(.ime acquainted have no 

 spinal column, but they do have a structure that takes 

 the place of it. This is a soft, flo.xitile rod, or cord, that 

 tapers to both ends and hes along the hack, where the 

 backbone lies in vertcl)rates. Again, a very few animals 

 — some sea squirts — possess this coi'd only in their youngest 

 stages, losing it entirel,y when full grown. Finally, all 

 vertebrates, as fish, Inrds, and mammals, possess this cord 

 in their embryonic stages, but its place, in most, is taken 

 later b}' a spinal column. Hence all animals, not included 

 in the eleven branches ;dready discussed, possess, either in 

 their youngest stages or throughout life, a soft, flexible 

 cord, or rod, known as a vntnehord, and conso(iuently they 

 are grouped tugcther in one bianch called Ihe Cliordnfa. 



Moreover, when any animal so far noted lias had a cavity 

 in the body, it has liad but one; for example, the hydra, 



200 



