300 PROFESSOR FRANK J. COLE 



massed dots in the more central portions of the gill. We have, in fact, a dejfinite 

 capillary system in the gills, although a somewhat coarse one. Near the circular margin 

 of the gill a few respiratory vessels may pass straight across from the afferent to the 

 efferent radial vessel without modification, as shown in fig. 6. The type of gill circula- 

 tion described above, carried much further, gives us the example of circulation found in 

 the gills of the lamprey as described by Favaro.* 



The branches of the afferent radial vessel do not usually pass straight across the gill 

 to become the factors of the efferent radial. Sometimes they do, and one can then 

 trace across the gill lamella a single vessel coursing from the afferent to the efferent 

 vascular side of the gill, and giving off anastomoses (about 50) as it goes along. But 

 more frequently the direct continuity is broken, and the branches of the afferent radial 

 interdigitate with the factors of the efferent vessel, as shown in fig. 6. 



In section it is easy to distinguish within the gill the branches of the afferent 

 branchial artery from the factors of the efferent branchial. The walls of both include a 

 few unstriated muscle fibres with long flat nuclei, but the lining of the afferent vessels is 

 very characteristic. Here we find, projecting into the cavity of the radial vessels and 

 their branches, large cells of varying shape separated from each other by distinct 

 intervals. They may project 12 m into the cavity of the artery, and are separated 

 by spaces of about 2"5 m, but sometimes by much wider gaps. At their base they 

 are about 10 m across. Each cell contains a large vesicular nucleus — sometimes two 

 — and the cytoplasm lodges a number of yellow brown particles not coloured by all 

 dyes, but staining black with iron hsematoxylin. 



These cells evidently constitute a blood " gland" of some kind. Giglio-Tos regards 

 the lymphoid tissue of the valvula spiralis of the Ammocoete as the source of both red 

 and white corpuscles of the blood ; but this view is attacked by AscoLi, who regards the 

 circulating blood of the Ammocoete as the formative sphere of the red corpuscles, as in 

 the embyro, and finds, as K. B. Shreiner has also done in Myxifie, the new corpuscles 

 dividing in the blood. Maas admits his inability to trace the source of the red 

 corpuscles of Myxine, and was not able to observe any early stages in the blood. He 

 states, however, that the body of these corpuscles, stained with iron ha^matoxylin, 

 exhibits numerous dark small accretions. I hope to be able to show in my next part 

 that the lining cells of the afferent vessels of the gills described above are the source of 

 the red corpuscles of the blood. 



Besides the afferent and efferent arteries the connective tissue of the gill lodges a 

 large number of irregular spaces, or lymphatics, having an inconspicuous but definite 

 lining with flat nuclei. Usually these spaces contain only a few blood corpuscles, but 

 they may contain many. They partially fill up in injected material. They are found 

 not only in the wall of the gill, but extend also into the coarser portions of the gill 

 laraellaj. On the side of the efl'erent gill duct the lymphatics communicate with the 

 peribranchial sinus (cp. Part IV, p. 221) by a large but short channel, which enters the 



* Atli Accad. tici. vend, treat, istr., 1905. 



