The StriTcture and Functions of the ha^molymph Glands and Spleen. 21 



observers. Involuntary muscle fibres (pi. I. flg. 9 i.m.f) and elastic 

 fibres occur in the lymphoid tissue, but by no means in large quantity. 

 Care must be taken not to confuse the elongated cells of the endo- 

 thelium lining the capillaries, which everywhere pervade the lymphoid 

 tissue, with involuntary muscle fibres. 



AVarthin^) states that he has found free red cells in the adenoid 

 tissue, but the presence of these cells is extremely doubtful. They 

 are certainly seen in the Ijanphoid tissue, but careful observation 

 reveals the fact that they are in capillaries, the walls of which are 

 often indistinct. Free red corpuscles in the adenoid tissue exist only 

 in places where the delicate endothelium is absent; whether this is due 

 to the breaking away of these endothelium cells to form phagocytes, 

 or whether they do not exist in these situations, it is difficult to say, 



Masses of dark yellow or brown pigment are seen frequently in 

 the adenoid tissues in the neighbourhood of thé sinuses, though such 

 masses are not so often seen in the case of the sheep as in the rat. 

 They are darker than the corresponding granules found within the 

 phagocytes of the sinus, probably on account of the greater accumulation 

 at these points, and of the fact that much of the pigment constituting 

 them is in a free state (pi. I. fig. 8). 



The various forms of cells found in the lymphoid tissue have 

 been fully described by more than one observer: for the sake of 

 completeness I append the following description given by Vincent and 

 Harrison-), which agrees more closely with my own observations than 

 does any other. 



"The foUomng cells were found: — 



1. The most numerous, small cells, 4 — ò i^i in diameter, almost 

 entirely composed of nucleus, but with a thin ring of protoplasm 

 (pi. I. fig. 9 leu). 



2. Cells with similar characters, but more abundant protoplasm. 



3. Cells larger than the preceeding, with large pale nuclei oval or 

 crescentic in form. 



4. Large multinuclear cells, containing as many as 7 or 8 nuclei. 



^) Loc, cit. -) Loc. cit. 



