THE ANCE8TBY OF VEUTEiniATEfi 



21J5 



(Fig. 281 , rich) . The nervous sys- 

 tem {hr and sp. cd) lies above tlie 

 cliorda ; it liegins in a sliglit en- 

 largement whose cavity communi- 

 cates with the exterior by a nasal 

 pit and carries a large pigmented 

 " eyespot " [e. sp). The blood 

 system consists of a ventral vessel 

 carrying blood forward and a flor- 

 sal one carrying it backward. 

 The ventral vessel connects with 

 the dorsal vessel by a pair of 

 vessels running along each gill- 

 arch {hr.sep, between the gill- 

 slits), and from the pharynx the 

 blood runs toward the tail. The 

 direction of the dorsal current in 

 the trunk of Amphioxus is thus ex- 

 actly opposite to that of worms. 

 There is a series of kidney tubules 

 {nph) much resembling those of 

 annelids, and the reproductive 

 cells are formed in glands that are 

 repeated in many segments of the 

 body. In Amphioxus, as in in- 

 vertebrates, the outcu' skin con- 

 sists of a single layer of cells, below 

 which lie cells of a connecting 

 nature. Finallj', on the exterior a 

 pair of folds, like fins, runs con- 

 tinuously from near the mouth to 

 the outer pore of the gill-chamljer. 



-ir 



-gtn- 



FiG. 2T'J. — Drawing of entire 

 Balanogiossus. /'/■, frills ; co, 

 collar ; (jen, genital ridges ; 

 hep, ridges lying over liver ; 

 7J7-, pro]>osris. From Parker 

 and Haswell ; after 8pengel. 



