First lesson in zoology : adapted for use in schools . eurrent, openings; «, nervous cord; ii, notocord: g, respiratory sac;n, sense-cavity containing the eye (o) and the ear (o). (Magnified.) minute animals, as the lancelet does, until, in their de-scendants, the notocord supported the entire body, and anincipient brain was formed, approaching that of the lance-let, imperfect as it is, and behold the backboned type oflife was established ! In the Balanoglossus worm, with its gill-slits in itspharynx, and the central nervoussystem situated above a notocord,we have a sign-post among worm-like a
First lesson in zoology : adapted for use in schools . eurrent, openings; «, nervous cord; ii, notocord: g, respiratory sac;n, sense-cavity containing the eye (o) and the ear (o). (Magnified.) minute animals, as the lancelet does, until, in their de-scendants, the notocord supported the entire body, and anincipient brain was formed, approaching that of the lance-let, imperfect as it is, and behold the backboned type oflife was established ! In the Balanoglossus worm, with its gill-slits in itspharynx, and the central nervoussystem situated above a notocord,we have a sign-post among worm-like animals pointing out the wayto the ascidians, the forerunners ofthe vertebrates. In the highest molluscs, such asthe cuttle-fish, we have anticipa-tions of the vertebrates in the prin- ^^ nerve-centres being gathered into the head and thereforming a large brain, which is partially protected by piecesof gristle, forming a slight brain-case; their eyes, moreover,are nearly as perfect as those of a fish. But the cuttle 142 MBST LESSONS IN ZOOLOGY. so to speak, an abortive attempt to reacli the yertebratelevel. It was given to some lonely worm, whose very fam-ily name and form are now lost, to found a chain of beingwhose links are now slowly, and with much painstakingsearch on the part ^ of naturalists, being picked up andbrought to light. Even after the lancelet came into being, the steps bywhich the genuine backboned family became recognized inanimal society were painful, and only in a degree successful Classes oj Vertebrates. 1. Toung with a nervous and dor-sal cord Tunieata. Ascidians. 3. No skull or brain; blood wbite-t«pfcif<wcZ««. Lancelet. 3. Notocord persistent; no jaw- bones; six to ten pairs of purse like gills Maraipobranehii.^Ijaxapteys. 4. Swimming by fins; with gills; (AL/vx-o-v, no claws Batraehia. AmphiManBr Frog,
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1894
