414 W. H. GASKELL. 



sequent diminutiou of the tendency to stagnation. In addi- 

 tion to this possible cause of narrowing of the bed of the 

 stream another factor in all probability comes into play, viz. 

 the formation of fibrous tissue around and amidst the pig- 

 ment masses. The presence of pigment in the walls and 

 trabeculse of the blood spaces is due to the circumstance 

 already noted, that all active cells seize on inert pigment with 

 which they are brought into relation. If, as may sometimes 

 happen, there is entire stagnation of a mass of these eflfete 

 blood-corpuscles, then the changes in this mass will correspond 

 in all respects to those met with in the organisation of a 

 thrombus, viz. the penetration and final replacement of the 

 blood mass by cells of connective-tissue nature ; the subsequent 

 contraction of this newly formed tissue, just as in the forma- 

 tion of a cicatrix would convert the original space which 

 contained the blood-corpuscles into a strand of pigmented con- 

 nective tissue. 



The process which is going on seems to me to be somewhat 

 as follows : — The effete blood-corpuscles heavy with pigment 

 do not circulate with the general circulating normal blood- 

 corpuscles, for the heart and ventral aorta are free from them. 

 They remain stranded in those parts where the current is 

 slow, and where, owing to the absence of fine capillary channels, 

 eddies and back currents must take place. In such places 

 they are apt to congregate and remain stationary against the 

 walls and septa of these spaces, thus forming a thrombus of 

 dead pigment-bearing corpuscles. By the growth and spreading 

 inwards of the connective tissue of the walls and septa this 

 thrombus becomes part and parcel of the walls against which 

 it is formed, in the same way as a thrombus becomes organised 

 in any other Vertebrate. With this organisation constriction 

 occurs, so that the original blood space is narrowed or oblite- 

 rated, and at the same time its walls become more and more 

 full of pigment-granules. These pigment-granules are partly 

 taken up by the cells of the connective tissue, but many are 

 doubtless lying free in the interspaces of the fibrous 

 bundles between the time of the death of the blood-corpuscles 



