266 BULLETIN OF THE 



grouped into nuclear membrane, and 1-3 dark-outlined nucleoli. All the rest 

 is a water-clear " Kernsaft." In the author's opinion the whole process is a 

 " post-mortem disintegration." 



ToRoK ('77) * has observed in living dermal cells of embryos of Siredon 

 that the " Dotterplattchen " suddenly change position, and that this locomotion 

 is more precise in proportion as the nucleus is more sharply differentiated. No 

 immediate relation exists between this phenomenon and changes of form on 

 the part either of the cell or its nucleus, inasmuch as the latter are not accom- 

 panied by any rearrangement of the yolk elements. It is concluded from the 

 study of osmic acid preparations that such Dotterplattchen movements re- 

 sult : (1.) Either in a group (or groups) of Dotterplattchen which melt together 

 more or less completely and give rise to a network ball (kugelformige Netzge- 

 bilde) which may occupy the same cell with one or several nuclei, or may take 

 the place of a nucleus. (!) This reticular structure is succeeded by fine fila- 

 ments having an irregular course, but the whole is not of the nature of a 

 permanent differentiation, and eventually disappears. Or (2.) in a radiate 

 arrangement of the Dotterplattchen about a centre of unknown significance. 

 This is succeeded by a grouping of the same elements into a circle. With 

 the widening of the circle there appear, as a differentiation of the central 

 ends of the Dotterplattchen (possibly with the participation of the homo- 

 geneous protoplasm), radial rods lengthening ultimately into fibres with an 

 increasing tendency to become curved (Stabchen-Faden). The Dotter- 

 plattchen disappear, and thus the whole cell loses its original character. 



Both these structures are only transitional manifestations of cells in process of 

 becoming tissues, and the " Stabchen-Faden " disappear earlier (in the embry- 

 onic life of the Siredon) than the " Netzgebilde." 



It is perhaps attributable to his firm belief in the total disappearance of the 

 germinative vesicle and in a like fate for the nucleus of embryonic cells, that 

 Torok failed to connect these remarkable changes with the process of cell 

 division (to which they so clearly belong), rather than with that of the 

 differentiation of cells into tissues. Yet it did not escape him that the dis- 

 appearance of the nucleus was accompanied with similar transpositions of the 

 " Dotterplattchen," only he maintains that in many cases they are independent 

 of each other, so that, while in one cell new formative centres arise in the 

 presence of a well-preserved nucleus, in another cell no trace of a nucleus of 

 w^hatever kind is to be found.-}- 



Of the changes in the nucleus, starting from the well- formed structure, Torok 

 says that a finely granular condition is followed by the appearance of coarser 

 granules and an increasing transparency of the " Zwischensubstanz," accom- 

 panied by an increase of the mass of the nucleus. Then the coarse grains 



* See also Torok, '74. 



t That new centres of attraction arise before a perceptible change takes place in 

 the nucleus is conclusively shown in the present paper, and has also been pointed out 

 by Strasburger ('76, p. 158) forlsoetes. 



