GILL-BARS 



423 



downwards, of a tongue-like process, the secondary gill- 

 bar or septum (Fig. 107, br. sep. 2),. so that in the adult 

 the slits and intervening bars are seen to be arranged 

 in couples, the supporting rods (br. r. 1} of the primary 

 A ' B 



air 



FIG. 109. Amphioxus lanceloatus. 



A, transverse section of the pharyngeal region ( x 15). a. dorsal aorta ; b. atrium ; 

 c. nofochord ; co. coelome ; e. endostyle ; g. gonad (ovary) ; kb. branchial 

 bars ; kd. pharynx ; /. " liver " ; my. myomere ; n. nephridium, shown as if 

 opening into the coelome ; r. spinal cord ; sn, sn. dorsal and ventral spinal 

 nerves. 



B, transverse section of the intestinal region, (x 20.) atr. continuation of atrium 

 on right side of intestine ; ccel. coelome ; d. ao. dorsal aorta ; int. intestine ; 

 myom. myomere ; nch. notochord ; neu. spinal cord ; 5. int. v. sub-intestinal 

 vein. (From Parker and Haswell's Zoology : A, from Hertwig, after Lankester 

 and Boveri ; B, partly after Rolph.) 



bars (br. sep. i) being forked below. A further compli- 

 cation is produced by the formation of transverse 

 connections supported by skeletal rods, between the 

 gill-bars. The gill-slits are more numerous than the 

 muscle-segments or myomeres (myom), and, owing to 

 their obliquity, a large number of them always appear 

 in a transverse section (Fig. 109, A) . 



