THYREOID GLAND OF THE TELEOSTS 737 



Where the follicles are densely packed, numerous spaces and 

 channels run between them. The smallest of these seem to have 

 no endothelial wall, so that the lymph flows directly against the 

 epithelium of the follicles. In other cases the lymph vessel is 

 indicated by two parallel endothelial lines running between the 

 foHicles. This does not agree with L. Miiller's view that the 

 blood capillaries are in close contact with the epithelium while 

 the lymph vessels are separated from the follicles by blood ves- 

 sels or connective tissue. The foHicles are sometimes, as de- 

 scribed in the anatomical part, situated directly on the big lymph 

 spaces around the ventral aorta as the text figures 4 to 7 show. 

 (See also pi. IV, figs. 2, 3.) 



In the conger eel and skate Baber was unable to detect the 

 lymph vessels. Since he injected the venous system which is 

 connected with the lymph vessels he thus regarded the lymph 

 capillaries as veins. Ferguson has been more successful in dis- 

 tinguishing between these two sets of vessels in the dogfish. 



In some instances, less often, however, than it occurs in higher 

 vertebrates, a substance was found in the lymph vessles, which 

 had apparently the same structure as the contents of the follicles. 

 The lymph spaces were filled with this substance in one instance 

 and showed many smaller channels running together into the 

 larger ones (pi. V, fig. 18, L). According to Anderson the colloid 

 in the lymph vessels undergoes a change, becoming diluted and 

 finely granular and is difficult to distinguish from blood serum. 



The way in which the colloidal material leaves the follicle 

 is not made clear by my study. Attention may be called to the 

 varying views of different authors, especially those of Biondi 

 and Anderson, given in their description of the follicular epi- 

 thelium. It must be mentioned also that Htirthle believes in 

 temporary intercellular channels which form between the cells 

 for the passing of the colloid. I saw in a very few cases a colloidal 

 pseudopodium, as it were, push through the epithelium. 



I am also unable to state from the thyreoid gland in the Tele- 

 osts whether the veins contain colloidal substances and carry 

 them into the circulation. 



