vin 



SKELETON AND GILL-BARS 



407 



are rod-like bars of a substance somewhat resembling 

 cartilage supporting the oral hood and cirri (Fig. 99, sk), 

 chitinoid rods {br. r) supporting the gill-bars between the 



A B 





coeZ 



s.iht.-w^ 



Fig. 100. — Amphioxns lanceolaius. A, transverse section of the pharyngeal region. 



a. dorsal aorta ; b. atrium ; c. notochord ; co. coelome ; e. endoatyle ; g, gonad 

 (ovary) ; hb.^ branchial septa ; kd. pharynx ; /. liver ; -iny. myomere ; n. nephri- 

 dium ; r. spinal cord : j«, j«, dorsal and ventral spinal nerves. 



B, transverse section of the intestinal region, atr. atrium ; cal. ccelome ; d. ao. 

 dorsal aorta ; int. intestine ; inyont. myomere ; nch. notochord ; neu. spinal cord ; 

 s. int. V. sub-intestinal vein. (From Parker and Haswell's Zoology : A, from 

 Hertwig, after Lankester and Boveri ; B, partly after Rolph.) 



clefts, and short rods of connective-tissue, the fi?i-rays, 

 in the dorsal and ventral fins (Figs. 98 and 99, dors, f.r, 

 vent f.r). 



In the course of development, each primary gill-slit 

 becomes divided into two by the growth, from above down- 

 wards, of a tongue-like process, the secondary gill-bar or 

 septum (Fig. 99, br. r. 2), so that in the adult the slits and 



D D 2* 



