The Structure and Functions of the haemolymph Glands and Spleen. 39 



are present, while in otiiers little reticnhini bnt numerous phagocytes 

 are found. 



In other glands he has observed many phagocytes, some spherical, 

 others shewing clear branched processes, which were in many cases 

 directly continuous with similar processes of reticulum cells. 



I am unable to entirely confirm this view of the origin of phago- 

 cytes, for as is now recognised, reticulum consists of fibres and not bran- 

 ched cells. Also, even if the reticulum were composed of branched cells, 

 the loss of these, when they were developed into phagocytes, would 

 leave the adenoid tissue almost entirely unsupported. It is much more 

 probable that the processes observed by Schumacher were those of 

 "endothelium cells attached to the reticulum" and that these cells give 

 origin to phagocytes. The second view has been advanced by Thome ^), 

 who believes that endothelium cells lining the capillaries are developed 

 into giant cells with phagocytic properties. He has observed certain 

 intermediate forms between endothelium cells of the capillaries and pha- 

 gocytes. The third view has been suggested by Drummond'^) who be- 

 lieves the cells are nothing more than enlarged leucocytes. He has 

 found a complete series of intermediate forms between ordinary leuco- 

 cytes and the hyaline cells under discussion. In one respect I am able 

 to confirm Drummond, in that certain of the intermediate forms he de- 

 scribed have been observed, such as smaller hyaline cells, and leuco- 

 cytes having more than the usual amount of protoplasm surrounding 

 them. But this is not sufficient evidence in support of the theory, 

 though it is certainly somewhat comparable to the statement by Köl- 

 liker-^), that ordinary leucocytes in the spleen grow, by feeding upon red 

 cells, into giant cells or phagocytes. There is no reason however why 

 this view should be abandoned, or indeed why all three processes should 

 not proceed side by side. I am inclined to the view that the endothelium 

 lining the reticulum^ capsule, adenoid tissue and capillaries is con- 

 tinuous, and thinh it highly prohahly that phagocytes may he developed 

 from any or all of its cells. In a haemal gland from an ox, I have ob- 

 served endothelial cells, containing the characteristic pigment, covering 



^) Log, cit. ^) Loc. cit. ") Loc, cit. 



