48 



ZOOLOGY 



SECT. 



lamella is supported towards its outer edge by one of the branchial 

 rods (Fig. 752, br. r.) already referred to. These are narrow bars 

 united with one another dorsally by loops, but ending below in 



free extr mities 



-J' which are alter- 



nately simple 

 and forked. The 

 forked bars are 

 the primary (br. 

 r. 1), those with 

 simple ends the 

 secondary (br. r. 

 2} branchial rods, 

 and the lamella; 

 in which they are 

 contained are 

 similarly to be 

 distinguished as 

 primary lamellcc 

 (br. sep. 1} and 

 secondary or 

 tongue-lamella; 

 (br. sep. 2). In 

 the young con- 

 dition the two 

 clefts between 

 any two primary 

 lamellae are re- 

 presented by a 

 single aperture : 

 as development 

 proceeds a down- 

 growth takes 

 place from the 

 dorsal edge of 

 the aperture, 

 forming, as in 

 Balanoglossus (p. 

 5), a tongue which 

 extends d o w n- 

 wards, dividing 

 the original cleft 

 into two, and 

 itself becoming a 



secondary lamella. A further complication is produced by the 

 formation of transverse branchial junctions or synapticulce, sup- 

 ported by rods connecting the primary septa with one another at 

 tolerably regular intervals. 



FlG.s753. Amphioxus lanceolatus. Diagrammatic transverse 

 section of the pharyngeal region, passing on the right through a 

 primary, on the left through a secondary branchial lamella. 

 ao. dorsal aorta ; c. derm ; ec. en dostylar portion of ccelome; /. fascia 

 or investing layer of myomere ; fh. compartment containing fin -ray ; 

 ff. gonad ; gl. glomerulus (modified part of branchial artery in 

 relation to nephridium) ; k. branchial artery ; led. pharynx ; Id. 

 combined atria! and ccelomic wall (ligamentum denticulatum) ; 

 m. myomere ; int. transverse muscle ; n. nephridium ; of. meta- 

 pleural lymph-space ; p. atrium ; so. ccelome ; si. ventral aorta ; 

 sk. sheath of notochord and neuron ; uf. spaces in ventral wall. 

 (From Korschelt and Heider, after Boveri and Hatschek.) 



