194 THE ORIGIN OF VERTEBRATES 
Fic. 81,—SAMPLES FROM A COMPLETE SERIES OF TRANSVERSE SECTIONS THROUGH 
THE THYROID GLAND OF AMMOCGTES. 
Sections 1 and 2 are anterior to the thyroid opening, Th. 0.; sections 3, 4, and 5 are 
through the thyroid opening; and section 6 is posterior to the thyroid opening 
before the commencsment of the curled portion. : 
Pe ee oe 
