i 9 4 



THE ORIGIN OF VERTEBRATES 



\ Tko 





4;- 





5 6 



Fig. 81. — Samples from a Complete Series of Transverse Sections through 



the Thyroid Gland of Ammocoztes. 



Sections 1 and 2 are anterior to the thyroid opening, Th. o. ; sections 3, 4, and 5 are 

 ■ through the thyroid opening ; and section 6 is posterior to the thyroid opening 

 before the commencement of the curled portion. 



