FIGURE NO. 6 



AMPHIOXUS OR THE LANCELET 



Near the beginning of the Vertebrate or Chordate 

 series, there is a class (Cephalochorda) of very primi- 

 tive animals — the lancelets. There are several different 

 kinds, and, like many old-fashioned types, they have 

 a wide geographical distribution. They are found in 

 many seas, spending much of their life buried in the 

 fine sand, the only part protruding being the ciliated 

 cirri (C) around the mouth. The cilia waft in micro- 

 scopic organisms. At times the lancelets bestir them- 

 selves and swim with an undulatory movement in the 

 water, utilizing their 62 or so muscle-segments or myo- 

 tomes (MY). They have the following Vertebrate 

 characters: — a dorsal nerve cord (spinal cord), a dor- 

 sal supporting axis or notochord (N), numerous gill- 

 slits, a segmented body (MY), numerous kidney-tubes 

 or nephridia. But they are in many respects primitive, 

 e.g., in having no skull, no jaws, no limbs, no brain, no 

 heart. There are 26 pairs of reproductive organs or 

 gonads (G). AT is the breathing aperture or atrio- 

 pore; CF, the caudal fin. 



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