208 JEREMIAH S. FERGUSON 



about the thyroid gland and can be demonstrated by injection and 

 in sections; they are true "vasa lymphatica." 



6. The blood-vessels within the thyroid gland terminate in a 

 network of ''venae lymphaticae" which invest the follicles, receive 

 the vasa lymphatica, and transmit either or both blood and lymph, 

 under varying conditions of blood-pressure. 



7. The thyroid artery arises from the ventral end of the efferent 

 hypobranchial arterial loop contained in the hyoidean hemibranch 

 and the adjacent half of the first holobranch by an independent 

 origin or by a common stem with the mandibular or submental 

 artery. 



8. The thyroid veins in these fishes for the most part enter the 

 ''thyroid sinus," a mass of veins and lymphatic vessels which pour 

 their blood into the hyoid sinuses. 



9. The rhythmic respiratory movements of the pharyngeal wall 

 cause the thyroid sinus to act somewhat after the manner of a 

 "vein-heart" or "lymph-heart." 



10. The hypobranchial arterial system is formed as described 

 by Hyrtl in 1858 and 1872, and the direction of the flow of its 

 blood is from the gill vessels toward the coronary and other ter- 

 minal arteries, as indicated by Hyrtl and again by Parker and 

 Davis in 1899, and not from the subclavian artery toward the 

 coronaries, as described by T. J. Parker in 1886. The hypobran- 

 chial artery of T. J. Parker, forming an anastomosis between the 

 subclavian and median hypobranchial arteries, is of insignificant 

 importance and is frequently wanting. 



11. The relative volume and distribution of the "colloid" in 

 the glands of different species indicates that this substance is a 

 retention product, formed from the albuminous secretion of the 

 follicular epithelium. 



12. The further changes occurring in the "colloid" indicate 

 the possibility of its usefulness as a sort of stored-up secretion. 



13. The follicular epithelium contains both "chief" and "col- 

 loid" cells, the latter being even more numerous and characteris- 

 tic than in the mammalian thyroid. 



14. The parenchymal epithelium is in intimate relation with the 

 vasa and venae l^^mphaticae; it rests directly upon or in close 

 proximity to the endothelial wall of these vessels. 



