THE EVIDENCE OF THE THYROID GLAND 21 7 



Ammocoetes in the shape of the peculiar large cells packed together, with 

 pigment masses in between them, which form such a characteristic feature of 

 the glandular-looking material, which fills up the space between the cranial 

 walls and the central nervous system. 



Finally, the relationship which has been known from time immemorial to 

 exist between the sexual organs and the thyroid in man and other animals, and 

 has hitherto been a mystery without any explanation, may possibly be the last 

 reminiscence of a time when the thyroid glands were the uterine glands of the 

 palaeostracan ancestor. 



The consideration of the facial nerve, and the segments it supplies, still 

 further points to the origin of the Vertebrata from the Palfeostraca. 



