ORIGIN OF JAW APPARATUS 379 
oxine jaw bars, which would be a peculiarly fit use to make of 
such building material. 
Fig. 29 Three figures to show the basic-similarity in the arrangement of the 
jaw apparatus in A. Amphioxus, B. Ammocoetes, C. Bdellostoma. 1 to 4 are 
five nerves of jaw apparatus. 
When the jaw is protruded the fourth tentacle lies above and 
upon the exposed dental surface, and when the jaw is being re- 
tracted the tentacular flap serves to clean the edge of the jaw 
of foreign particles. 
