(n6) 



t.m 



bEd. 



Fig. 79. A, Transverse section of endostyle of ammocoete larva. 



cav. cavity of the gland; cil.g. ciliated groove in floor of pharynx; lam. lamellae of gills; 

 ph. cavity of pharynx; seer, mucus-secreting cells of the gland. 



b, Transverse section of thyroid follicles of adult. (After Young and Bellerby.) 



C, Cross section of endostyle of ammocoetes larva of Petromyzon tnarinus at level 

 where it is connected by a duct to the pharynx. Autoradiograph showing distribu- 

 tion of protein-bound I 131 . The radioactive clumps of cellular debris in the 

 glandular lumen and in the duct suggest that the material represents a holocrine 

 secretion, which will probably be absorbed in the intestine. 



d. duct; hs. cellular debris; ph. pharynx; t II d. type II dorsal cells; 

 t III epithelial cells, 



