INVER'TEBRA'TA I Neo-1 at. non). pl.. from Lat. in-, not ro ITI1111 rertrbro, joint, from rerierc. Ski !wt./. ()Church Slay. mule!:, to turn, (loth. orairPon, irenr Nt. ( )1 11;„ irfT11(111,CCr. 111•1711 II, to become ) . Ani mals which do not have a vertebral eolumn or spine. The term is used in contrast with Ver tebrata (q.v.), or animals with a backbone. One group, then, is formed on positive and the other 011 negatiVe characters. Before the anatom ical structure and the embryological develop ment of animals was very generally worked out, the barrier between invertebrates and verte Ill.:Iles was supposed to be absolute; but with the refinement of anatomical and embryological methods of study, brought about in a great measure by the use of the miero•cor, the hiatus lwtween them is nearly bridged over. Aseidians are now considered to be degenerate :investors of vertebrate-.: some of the nemerteall and
eloatoprod worms approach vertebrates iu eertain characters, and Balanoglossus and rephalooliseus (q.v.) are frequently called lietni-ellordata (see I, because they are so near the boundary line between vertebrate: and inver• tebrates that they ran he said to be only half vertebrates. \nil not only has this barrier been broken down, but. with our increased knowledge. the absolute independence and isolation of many different groups of invertebrate animals which the earlier systematists believed to exist 11311st he abandoned. The foundation of the zo;dogy of these animals as there defined. was laid 1)7 Lamarck (q.v.) in a monumental work. Systime deR aninanrr,r NanR meat tires. published in Paris in 1g01; followed in 1g15-22 by Ilistoiror nn turdle (leg Illihnollr SOUS rerifforr.c.