420 



THE LANCELET 



CHAP. 



(Fig. 107, neb) 

 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 olfactory, 

 optic, or auditory 

 organs. The 

 pharynx is rela- 

 tively very large, 

 and is perforated 

 by very numerous 

 oblique gill-slits 

 (br. d), which do 

 not open on the 

 exterior directly, 

 but are surrounded 

 by a chamber, the 

 ati'ium (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 

 development from 

 the branchial 

 chamber of the 

 tadpole (p. 207), 

 has somewhat 



