MIL 



PHlftAJM CHORDATA 



given off a blind pouch, 

 the liver (Ir.) or hepatic 

 ccecum, which extends 

 forwards to the right of 

 the pharynx : it is lined 

 with glandular epithelium 

 and secretes a digestive 

 fluid. 



The gill-slits (br. cl) 

 are long narrow clefts, 

 nearly vertical in the 

 expanded condition, but 

 very oblique in preserved 

 and contracted specimens 

 hence the fact that a 

 large number of clefts 

 always appear in a single 

 transverse section (Fig. 

 751, A, kd.). The clefts 

 are more numerous than 

 the myomeres in the 

 adult, but correspond in 

 number with them in the 

 larva : hence, they are 

 fundamentally m e t a - 

 meric, but undergo an 

 increase in number as 

 growth proceeds. 



The branchial lamella 

 (Fig. 752, br. sep., Fig. 

 751, A, Jcb.), or portions 

 of the pharyngeal wall 

 separating the clefts from 

 one another, are covered 

 by an epithelium which 

 is for the most part en- 

 dodermal in origin, and 

 is composed of greatly 

 elongated and ciliated 

 cells. On the outer face 

 of each lamella, however, 

 the cells are shorter and 

 not ciliated, and are, as a 

 matter of fact, portions of 

 the epithelial lining of 

 the atrium, and of ecto- 

 dermal origin. Each 



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