516 MR. F. E. BEDDARD ON THE DEVELOPMENT AND [DeC. 7, 



by their smaller size, by their very deeply stained protoplasm, and 

 by the fact that they nearly always contain a large number (3-5) of 

 small nuclei close together. I have not yet succeeded in detecting 

 these cells in the follicular layers, but I am nevertheless inclined to 

 think that they are migratory leucocytes. I am at a loss, however, 

 to account for the almost universal division of their nuclei into four 

 or five. 



The presence of leucocytes in almost all the tissues and glands 

 of the body is so well known that I need not give any detailed 

 references ; the presence of these cells is not, however, to be con- 

 founded with the migration of follicular cells. If, however, the 

 identification of the follicular epithelium with a layer of immigrated 

 leucocytes be right, there can be no distinction between the two pro- 

 cesses. The observations recorded in this paper, however, plainly 

 show that in Protopterus at least there can be no possible confusion 

 between follicular cells and lymphoid corpuscles, which is contra- 

 dicted bv so many other developmental facts. Unless it can be 

 shown that lymphoid cells may arise from the direct metamorphosis 

 of germinal epithelial cells it is quite absurd, in the present case at 

 any rate, to allow any homology between follicular cells and im- 

 migrated white lymph-corpuscles. 



Stage III. — In this stage (figured diagrammatically in fig. 3, plate 

 xxviiii. of my former paper) the follicular epithelium is undivided 

 from the ovum by any trace of membrane ; the cells of which it is 

 composed have dwindled down to a single layer ; their diameter bears 

 a verv small proportion to that of the enclosed mass of yolk, which 

 has enormously increased in size. The cells of the follicular epithe- 

 hum are still filled with yolk-spherules presenting no differences 

 from the yolk-spherules which make up the substance of the con- 

 tained mass. Their nuclei are conspicuous and round in shape. The 

 follicular cells appear to continue to take a share in the nutrition of 

 the body from the fact that they are large and well developed, and 

 that the interstices of the protoplasmic network are largely filled with 

 yolk- spherules : occasionally (e. y. figs. 7, 8, a) the nuclei of the folli- 

 cular cells showed signs of degeneration ; this is probably preliminary 

 to the evacuation of the cell-contents into the interior. Here and 

 there the follicular cells appeared to be proliferating, the budded-off 

 cells moving into the interior ; two such instances are shown in figs, 

 7, 8. It is of course a difficult matter to decide how far the appear- 

 ances shown in the two figures cited are due to the proliferation and 

 migration inwards of the follicular cells ; they might be explained, 

 by reference to earlier stages, as central cells which have still re- 

 mained in contact with the folHcular layer, only that they occur on 

 all sides, and it has already (p. 51 1) been stated that the central cells 

 are only in contact with the peripheral for a limited area. On the 

 other hand, a careful comparison of the example from which fig. H 

 is taken with another in pretty much the same stage of development, 

 only younger, as evinced by its smaller size, reveals the important 

 fact that the larger contains, in any given section, a larger number of 

 cells in its interior than the smaller. The larger was rather more 



