THE AMPHIOXUS. 



9 



4 



k 



th& difference between the extant Tape-worms and Ringed 

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

 regard the extant Appendicular ia as a last remnant of the 

 Chordoma 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 

 forms, which branched off from the worm 

 tribe in entirely different directions. When, 

 in a previous chapter (IX.), the vertebrate 

 nature of man was proved, it was incidentally 

 mentioned 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 

 (Arthropoda), Star-animals (Echinoderma), 

 and Soft-bodied Animals (Mollusca), like 

 the vertebrate tribe, originated from the 



Fio. 189. — Lancelet (Amphioxvs lanceolatus), 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 ; o, anal open- 

 ing; c, ventral opening (Poms abdominalis) ; d, gill- 

 body ; e, stomach ; /, liver-coecum ; g, large intes- 

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

 k, ixches of the aorta ; I, main gill-artery ; m, swellings 

 on its branches ; n, hollow vein ; o, intestinal vein. 



