ORIGIN OF JAW APPARATUS 359 
quick-acting reagents (e.g., osmic acid) it often happens that 
the velar tentacles are not all withdrawn and some of them still 
project forward (fig. 11), while others project backward. In 
life the velar tentacles were long ago observed to occasionally 
flip back and forth while the velum was fully expanded. Their 
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Fig. 13 Part of the brain and the terminal and septal nerves of Amphioxus. 
Two branches of the latter supplying the anterior end of the jaw apparatus are 
shown. 
normal position while the food current is flowing in through the 
velar aperture is that of full erection projecting forward into 
the oral hood, forming a funnel-shaped fence about the velar 
mouth. In the normal closure of the velum the tentacles are 
folded toward the center and caudad due to the fact that the 
