238 PROFESSOR MARSHALL AND EDWARD J. BLES. 



afferent vessel, and is continued beyond it, in the dorsal wall of 

 the pharynx, forwards and inwards towards the dorsal aorta ; its 

 most dorsal portion turns slightly backwards and opens into the 

 dorsal aorta. It receives numerous efferent vessels from the internal 

 gills, and opposite the dorsal end of the afferent vessel a small vessel 

 returning blood from the external gill. 



The ventral end of the efferent vessel is now directly continuous 

 with the lingual artery ; the difference between this stage and the 

 preceding one being clearly shown by a comparison of Figs. 13 and 14 

 with Figs. 11 and 12. The bulb-like enlargement of the lingual 

 artery, that was noticed at the earlier stage (Fig. 1 2, A L), is still 

 present, and it is by growth of the posterior branch of the artery 

 towards the end of the efferent vessel, E F.I, that the two vessels 

 meet and become continuous with each other. In front of the 

 swelling, the lingual artery runs forwards and then inwards along 

 the floor of the mouth, ventral to the first branchial and hyoidean 

 cartilages, and then onwards to the lower jaw (Figs. 13 and 14, A L). 



In some, but not in all, specimens of this age, there is a direct 

 communication between the afferent and efferent vessels of the first 

 branchial arch. This communication, which is shown in Figs. 13 

 and 14, is effected between the base of the afferent vessel and the 

 part of the efferent vessel immediately dorsal to the bulb-like swelling 

 on the lingual artery. At this point the afferent and efferent vessels 

 lie close together, but separated by a thin plate of deeply staining 

 cells, apparently epithelial in nature. Through this plate, the thick- 

 ness of which is rather less than the diameter of the vessels at this 

 part, a narrow and somewhat irregular channel runs, which connects 

 the vessels directly together. We have found it extremely difficult 

 to determine the exact time and mode of establishment of this 

 connection. In some specimens it is effected as just described by a 

 narrow and very short channel ; in others the two vessels lie very 

 close together, and a hole in the septum between them places them in 

 direct communication with each other ; while in others of the same 

 size, and apparently at the same stage of development, we have 

 failed to find any communication at all. 



d. The Second Branchial Arch. — Excepting the absence of any 

 vessel corresponding to the lingual artery, the vessels of the second 

 branchial arch agree very closely with those of the first. The afferent 



