CHORD. VIA 



269 



end of which is modified into a simple brain. On the anterior 

 surface of the brain is an unpaired pigment spot, the organ ol 

 sight. Ventral to the notochord is the alimentary canal, of 

 which the anterior portion 

 forms a long pharynx with 

 very numerous gill slits in 

 its walls. There are two 

 rows of these slits, a row 

 on each side of the body, 

 and instead of opening 

 directly to the outside, 

 they open into a chamber, 

 the atrium, which commu- 

 nicates with the outside 

 through the atrial pore 

 already mentioned. Pos- 

 terior to the pharynx is 

 the intestine, from the 

 anterior end of which a 

 diverticulum arises, di- 

 rected forward and to the 

 right, called the liver. 

 Excretory organs occur 

 in the region of the "ill 

 slits, and the germ-glands, 

 or gonads, lie in two Ion- 

 right 



gitudinal series, a 

 a left, on the 



& 



and 



inner 



walls of the atrial cham- 

 ber, into which the germ- 

 cells pass when mature, 

 and so out through the 

 The sexes 



atrial pore, 

 are separate. 



The muscles are very 

 well developed on each 

 side of the body. They are divided up into segments, or myo- 

 meres, which are shaped like hollow wedges fitting into one 

 another, with the point of the wedge directed forward. There 



