THE EVIDENCE OF THE THYROID GLAND 217 
Ammoceetes 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 
paleeostracan ancestor. 
The consideration of the facial nerve, and the segments it supplies, still 
further points to the origin of the Vertebrata from the Palwostraca. 
