278 BULLETIN OF THE 



Not being able to gain access to Schneider's paper (73) on Mesos- 

 tomum, I am indebted to the citation in Biitschli ('76, p. 399) for the 

 synopsis which follows. 



In the fecundated summer egg first the outline of the nucleus, which 

 Schneider holds to be the original germinative vesicle, [apparently]* 

 disappears, the nucleolus alone remaining visible. Acetic acid, how- 

 ever, brings out the much bent and folded outline of the nucleus. 

 Finally the nucleolus disappears, and the whole nucleus is converted 

 into a mass of finely curled fibres (Faden), which become apparent 

 [only] upon application of acetic acid. In place of these thin fibres 

 thick cords (Strange) finally appear, at first irregularly, afterwards ar- 

 ranged in a rosette which lies in a plane (equatorial) passing through 

 the centre of the sphere. These cords appear to form the outline of a 

 flat, much-indented vesicle ; however, by more careful observation one 

 becomes convinced that its contour is often interrupted at the inner 

 angles of the folds. t The granules of the egg have become grouped in 

 planes which intersect each other in a line perpendicular to the middle 

 point of the equatorial plane. Little of this arrangement is to be seen 

 on the fresh egg, but it becomes prominent on those treated with acetic 

 acid. When the cleavage begins the cords have increased in number 

 and have become so arranged that part are directed toward one pole, 

 the rest toward the other pole. Finally, the egg is fully constricted, 

 and the cords pass into the daughter cells. The rows of granules stretch 

 out and may be followed from one cell into the other. Biitschli does 

 not hesitate, after examining the figures, to identify the " cords " with 

 the " Kernplatte " and its lateral halves. According to him the inter- 

 zonal fibres are also indicated in the figure. The same method of 

 nuclear increase was observed by Schneider in the case of germ-cells of 

 spermatozoa and numerous other cells of Mesostomum, as well as in the 

 eggs of Distomum cygnoides.J 



* p. S. — The words enclosed in brackets I have interpolated since consulting 

 the original paper. 



t This description recalls in a vivid manner the figures which Flemming has quite 

 recently given of the nuclear metamorphosis of tissue cells in the case of the sala- 

 mander. 



I P. S. —Since writing the above, Schneider's paper {'73, pp. 113-118, Taf. V. 

 Figs. 4. h, 5 - 8, 11) has been secured. Besides assenting to what Biitschli says respect- 

 ing the identity of the "cords" and the lateral halves of the Kernplatte, there are 

 one or two points to which I would call attention. The interzonal filaments are rep- 

 resented in Schneider's Fig. 5. e (Taf. V.) as having each three thickenings, which col- 

 lectively form, in optical section, three parallel bands of thickenings lying between 



