The gerin-cclls. 661 



surmises as to their nature and fate. The former, as might be ex- 

 pected, is masterly. If one may judge from the brief reference to them 

 in his recent memoir, Rückert does not at present see his way to 

 any definite statements as to their nature and fate. That yolk-laden 

 cells, some of them of rather large size, are concerned in the formation 

 of the first blood-vessels and blood-corpuscles — the latter being 

 rounded (Minot), and not oval — is a fact not to be gainsaid. 



The writer has devoted some attention to this point, for during 

 the present investigation the work on the thymus and the first leuco- 

 cytes has not been forgotten. 



From Rückert's account of them it is difficult to say what a 

 megasphere is, or to apply his description to the mass of cells under 

 the blastoderm of such an "embryo" as No. 434. Of Torpedo-emhryos 

 of this very period Rückert defines the megaspheres as follows: 

 "Scattered between these elements there occurs a second form of cells 

 (megaspheres), characterised by their rounded form, theii' varied, mostly 

 very considerable size, their wealth of yolk-particles, and very hetero- 

 geneous, often peculiarly arranged nuclear contents". He notes their 

 abundance in the immediate neighbourhood of the germinal-cavity; 

 and further on, as in his latest work (where it is only suggested as 

 possible) he identifies them with merocytes, budded off from the yolk 

 ('87, p. 162). 



In this point it may be doubted, whether research will confirm 

 Rückert's surmise. It would, indeed, be remarkable, after what he 

 himself has recently established concerning the repulsion exercised by 

 cells of the blastoderm on the merocytic nuclei of the extra-spermato- 

 zoa, were any of the merocytes to get into the embryo ('99, p. 677 

 to 692 etc.). 



In some other particulars our results are in total agreement. 

 These concern the formation of nests of cells (concentric corpuscles) 

 in certain megaspheres, the frequent tendency of the nuclei to free 

 themselves of the burden of the yolk, and, at a date soon after 

 Flemming ('85, p. 223) had established and defined "chromatolysis", 

 he described the process (p. 165) in many of them, while failing to 

 identify its nature or its correspondence with the phenomena, recorded 

 by Prof. Flemming concerning the degeneration of certain germ- 

 cells. 



The connection of the megaspheres with blood-formation he found 

 in the well-known knob on the blastoderm of Torpedo. From my 

 own observations on this structure any relationship to blood-formation 



