325 



for example in Pleurouectes. The most anterior alveoli are found in 

 the middle line over the club-shaped muscle and in the reticular 

 tissue between the superior chondroidal bar and the oesophagus. This 

 is in the region of the first gill sack, which overlaps the club-shaped 

 muscle in front, but is anterior to the ventral aorta. Most of the al- 

 veoli however are found in the column of fatty reticular tissue which 

 occurs in the middle line between the internal surfaces of the gill sacks 

 laterally and the oesophagus and ventral aorta vertically. I have never 

 seen any alveoli ventral to the cardiac aorta. 



Vascular System. 



In addition to the definite blood vessels Myxine possesses a system 

 of large lacunar spaces, such as the extensive sub-dermal cavity, the 

 spongy tissue of the head, the peri-branchial sinuses, etc., which have 

 been generally regarded as belonging to the lymphatic system. I have 

 however long been convinced that these spaces were in communication 

 with the blood vascular stream. Jackson i), in his work on the vas- 

 cular system of Bdellostoma, mentions the passage of injection mass 

 from the vessels into the lymphatics, but believes the connection be- 

 tween the two to have been an artificial one, since he does not find 

 red blood corpuscles in the lymphatics in fresh and uninfected material. 

 If this is true then Myxine is greatly different, as blood is invariably 

 to be found in the lymphatics in living material. Ewart^), in his 

 paper on the vascular peribranchial spaces in the Lamprey correctly 

 appreciates the situation, and explains the general appearance of blood 

 in these spaces by connections between them and the internal jugular 

 vein found by him. 



I shall enter fully into the morphology of these spaces in my 

 fourth part on the vascular system of myxine. In the meantime I may 

 mention that I have discovered projecting from the posterior surface 

 of each afferent branchial artery at the place where this artery enters 

 the gill sack one or more papillae, and I have found these in every 

 specimen which has been dissected for them. On cutting serial sections 

 of several of these papillae it is seen that the base of each is widely 

 excavated, and is in fact an evaginated portion of the cavity of the 

 artery, whilst from this excavation there passes to open on to the 

 exterior one or more fine channels lined by epithelium. The calibre 

 of these channels is usually only slightly in excess of the width of 



1) Journ. Cincinnati Soc. Nat. Hist., Vol. 20, 1901. 



2) Journ. Anat. and Physiol., Vol. 12. 



