THE AMPHIOXU& 



91 



11 



111 



fch* difference between the extant Tape- worms and Ringed 

 Worms (Annelida). Moreover, in a certain sense we may 

 regard the extant Appendicularia as a last remnant of the 

 Chordonia class. 



We have now studied the most import- 

 ant animal forms which occur in the pedigree 

 of the human race, and which, in the zoo- 

 logical system, must be classed among the 

 Worms. In leaving this lower class, and 

 tracing our ancestry henceforth exclusively 

 within the vertebrate tribe, we at once ^ 

 leave behind the great majority of animal 

 (brms, which branched off from the worm 

 Liibe in entirely different directions. When, 

 ill a previous chapter (IX.), the vertebrate / 

 ature of man was proved, it was incidentally 

 entioned that the very great majority of « 

 animals are in no way directly allied to our , 

 tribe. The parent-forms of the three other ' 

 higher Animal tribes,the Articulated Animals 

 {Arihro'poda), Star-animals (Echinoderma), 

 and Soft-bodied Animals (MoUusca), like 

 the vertebrate tribe, originated from the 



Fig. 189. — Lancelet (^Amphiomus Icmceolatus), twice 

 the actual size, seen from the left (the longitudinal 

 axis is represented vertically, the mouth turned up- 

 ward, the tail downward, as in Plate XI. Fig. 15) : 

 a, mouth-opening, surrounded by cilia ; h, anal open, 

 iug ; c, ventral opening {Porus ahdominalia) ; d, gill- 

 body I 0, qtomach j /, liver-coecum ; g^ large intes- 

 tine ; h, coelom : », notochord (under it the aorta) ; 

 k, trches of the aorta ; I, main gill-artery ; tn, ewellingi 

 on its branches; n, hollow Tttiii} 0, intoitinal Tttin. 



