420 



THE LANCELET 



is 5^ OS 'JS . "" <D 



a 2 W) u xi "d ^ 



l-^ rfli1-s 



1 ^-o^l^ 



chord (Fig. 107, 

 ncJi) extends to the 

 anterior end of the 

 animal, and there 

 are no paired limbs. 

 A brain (br) can 

 hardly be said to be 

 present, and there 

 are no paired olfac- 

 tory, optic, or audi- 

 tory organs. The 

 pharynx is relatively 

 very large, and is 

 perforated by very 

 numerous oblique 

 gill - slits (br. ct), 

 which do not open 

 on the exterior 

 directly, but are sur- 

 rounded by a cham- 

 ber, the atrium 

 (Figs. 107, atr, 

 and 109 A, b) ; this 

 opens externally by 

 a pore (Figs. 106 

 and 107, atrp\ and 

 though differing in 

 its mode of deve- 

 lopment from the 

 branchial chamber 

 of the tadpole (p. 

 207), has somewhat 

 similar relations. 

 There is no heart 



