294 



ZOOLOGY 



straight food-canal, in the anterior part of which there are 

 numerous openings to the exterior — the giU-shts. There is 



a smaU sac, Ij'ing dorsal to the 

 ]Dharynx, which is regarded 

 as a chorda. The brain is 

 dorsal, and there are both 

 dorsal and ventral nerves. 

 If Balanogiossus is indeed a 

 chordatc, it is a degenerate de- 

 scendant of a primitive form. 

 Above the tunicates, and 

 sho^^dng the clearest possible 

 afHnities to the fishes, is a re- 

 markaljle animal about 5 cen- 

 timetres long. It lives almost 

 buried in the sand of the sea- 

 shore in various parts of the 

 world, and is known as Am- 

 phioxus (Fig. 280). It is 

 Ijilaterally sjanmetrical, or 

 nearly so, and has a distinctly 

 segmented body. The food- 



FiG. 27s. — .Balaiioy:Iossus, the arorn- 

 tongued worm. The proboscis at the 

 anterior end is at the top of the figure 

 (partly outside) ; behind it is an or- 

 ange-colored collar : then follows the 

 long, hrown-red trunk. Nat. size. 

 Photo, of living animal I ly W. H. C. P. 



canal runs nearly straight 

 through the Ijod}^ and is 

 ]5erf orated in the pharjmx 

 l;)y 90 or more pairs of gill- 

 slits. These do not, however, 

 open directljr to the exterior, but into a large chaml)er that has a 

 single posterior connection with the outer world. Through the 

 axis of the liody, from the ti)^ of the snout to the end of the tail, 

 runs the chorda, which, in this animal, is a sort of jelly-like rod 



