91 



internal (with respect to the middle line of the gill arch) 

 sides of the filaments. These are the afferent filamentar 

 vessels (4, A. and B.), and they are connected with the 

 afferent branchial vessels which run in the fused bases of 

 the filaments outside the tunnel referred to. If, on 

 the other hand, the system is injected from the dorsal 

 aorta, a second series of vessels which run down on the 

 outer surfaces of the filaments becomes visible ; these are 

 the efferent filamentar vessels, and they are connected 

 with the efferent branchial vessels which run in ihe tunnel 

 on the convex surface of the arch. At regular intervals 

 along its course the afferent filamentar vessel gives off an 

 arterial twig on either side of the axis of the filament 

 which passes into the respiratory lamellie (4, B). 



Text-fig. 4, B. represents a surface view of two 

 lamelliBe, the transverse section of the filament passing 

 throuffh the axis between two such lamellae. In a 

 fortunate injection of the branchial system it will be seen 

 that the lamellar branches of the aft'erent filamentar vessel 

 on entering the lamellse immediately break up into very 

 close capillary networks. This capillary network, seen 

 from the side, is represented by the transverse black lines 

 connecting the two filamentar vessels in 4, A. Each 

 lamella has a wall which at the base is composed of cubical 

 cells, but which over the flat surfaces is a thin squamous 

 epithelium. Within the space enclosed by this wall is the 

 capillary network, and no other tissues. According to 

 Plehn* the blood flows in spaces hollowed out of adjacent 

 closely-fitting cubical cells. The capillaries have not the 

 ordinary epithelial wall characteristic of such vessels. 

 After having: traversed this network the blood is received 



* Zuiu feineren Bau der Fischkieme. (Vorl. Mitth.) ZooL, Anz, No. 64f- 

 24 Bd., pp. 439-443, 1901. 



