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. A of the primary 

 A B 



FIG. 109. Amphioxus lancdoatus. 



\, transverse section of _the pharyngeal region ( 15). a. dorsal aorta : b. atrium ; 

 c. notochord ; co. ccelome ; e. cndostyle ; 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. ( : 20.) air. continuation of atrium 

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

 myom. 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.) 



bars (br. sep. /} 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). 



