118 CEPHALOCHORDATA CHAP. 
or alternate bending of the body from side to side in swimming 
or burrowing can be performed. There are usually, on each side, 
9 
=> 
= 
= 
=> 
—— 
= 
= 
A 
Be: 
ows 
SF 
J 
Fic. 72.—Branchiostoma lanceolatum. Diagrammatic transverse section of the pharyn- 
geal region, passing on the right through a primary, on the left through a secondary 
branchial lamella. ao, Dorsal aorta ; c, dermis ; ec, endostylar portion of coelom ; 
J, fascia, or investing layer of myotome ; 7h, compartment containing fin-ray ; g, 
gonad ; gl, glomerulus ; 4, branchial artery ; #d, pharynx ; /d, combined atrial and 
coelomic wall (ligamentum denticulatum) ; m, myotome ; mt, transverse muscle ; 
n, nephridium ; 7.ch, notochord; of, metapleural lymph space; p, atrium; sc, 
coelom ; si, ventral aorta; sk, sheath of notochord and spinal cord (sp.cd) ; uf, 
spaces in ventral wall. (From Korschelt and Heider, after Boveri and Hatschek.) 
29 myotomes in front of the atriopore, 14 between the atriopore 
and the anus, and 11 postanal, making 60 in all: some species 
have only about 50 myotomes, and some as many as 85. (See 
2 altace Sell 
