460 DR THOMAS H, BRYCE ON 
This account is different from that given by Frtix* of the development of the 
corresponding tissue in the Salmonidee. He derives the tissue from proliferation from 
the wall of the vein, and he describes and figures trabeculee of epithelioid cells which — 
give rise to the tissue, the cells in places becoming converted into both white and red 
elements. I have not seen appearances like these in Lepidosiren. In the early stages 
there is no sharp separation of the tract laden with lymphoid cells from the general 
mass of the mesenchyme, and all the indications are in favour of the view that it is 
merely a tract of the general mesenchyme in the spaces of which, for physiological 
reasons, the lymph cells are congregated. § 
This lymphoid tissue in the larval kidney is the rudiment of a very remarkable 
mass of lymphoid tissue in the cortical part of the adult kidney. It forms a thick cap, 
so densely filled with pigment that the structure is quite concealed, but it can be seen 
that it is thickly studded with leucocytes. t 
Lymphoid Tissue in Gut Wall. 
The fact that G1cL10-Tos { describes the spiral valve as the hemopoietic organ in the 
lamprey directed my attention specially to that structure in the later larval stages. 
I find that the fold is occupied by a denser tissue than that investing the gut. The 
small elongated nuclei proper to the tissue are more closely packed, while the free 
lymphoid cells or leucocytes are much less numerous. 
The tissue of the spiral valve does not then differ in kind from the general investing 
tissue of the gut wall, and so far as the larva is concerned there are no appearances 
suggesting that it has a special hemopoietic function. 
The number of leucocytes in the connective tissue investing the gut is very great. 
They lie in the meshes of a loose alveolar reticulum, and belong to all the different 
categories. There are large numbers of mononuclear cells, here in every probability, 
leucoblasts. Mitotic figures occur frequently. Cells with all degrees in the meta- 
morphosis of the nucleus, and with granules of all the varieties already mentioned, are 
very plentiful. Just as in the case of the kidney, this tissue represents, doubtless, the 
early stage of the lymphoid tissue surrounding the gut and occupying the spiral valve 
of the adult animal. This tissue is probably purely lymphoid—or, rather, the free cells 
are probably all lymphoid elements. There are no vessels to be seen crowded with 
erythroblasts, such as one would expect to find if the tissue had any relation to the 
formation of red cells. 
Before closing the descriptive part of my paper, I must refer to the condition of the 
thymus gland at this stage. I have not studied the early stages of its development, 
but I now find it as a small organ, cut up into lobes by the passage through it of 
muscular fibres and a nerve cord. The cells of the gland are now free from the 
* Loc. cit. + See paper by Granam Kerr, Proc. Zool. Soc., 1901-2. 
£ Arch. Ital. de Biologie, vol. xxvii., 1897. § Cf. ZinGLER, loc. cit., 1892, note, p. 21, 
