522 CELL DIVISION IN EGGS OF CREPIDULA. 



was reduced to at most 7 mil. amperes, and in several cases to 5, 2, or 1 mil. 

 ampere. The duration of the current varied from 15 minutes to 1 minute and 

 the eggs so treated were fixed either at once or from 1 to 60 hours after they had 

 been returned to dishes of sea water. Ah of these experiments are catalogued 

 as Nos. 1100-1143, at the end of this paper. 



Many eggs placed between the graphite plates show the effects of pressure; 

 many of those shown on Plate XL VIII are of this sort. The abnormalities in 

 the positions of the spindles shown in figs. 68-74 are duplicated in the pressure 

 experiments, while the dislocation of cells shown in figs. 75, 78, and 79 are also 

 very similar to those shown in the pressure experiments. Figs. 76 and 77 

 represent eggs which were pressed between glass plates, whereas all the other 

 eggs shown on Plate XLVIII were subjected to the electric current between 

 graphite plates. 



Many of the eggs used in these experiments were killed and their membranes 

 dissolved; others, on the other hand, developed normally. The earlier stages 

 of cleavage usually suffered much more than the later ones. In general, the 

 most characteristic effect of the current is found in the massing of chromatin 

 within the nuclear vesicle, as in synapsis, or in the failure of the daughter nuclei 

 to become vesicular. Indeed the latter may remain perfectly dense spheres. 

 In some cases, the polarity of the egg or of the cleavage cells seems to be lost and 

 the usual sharp separation between yolk and cytoplasm disappears. Sometimes 

 the direction of the spindle is abnormal. The eggs shown in figs. 80-93, Plate 

 XLIX, iUustrate some of the most common abnormalities observed in eggs sub- 

 jected to the electric current. In all of these eggs, the boundaries between 

 cytoplasm and yolk are but faintly marked; the nuclear membranes are usually 

 very thin or altogether lacking and the chromatin is massed within the nucleus 

 or scattered in clumps through the cytoplasm where it dissolves and disap- 

 pears, figs. 80-86. In some cases tetrasters are present (fig. 87), but these are 

 probably due to other causes than the electric current. In a few instances, 

 chromosomes have entirely disappeared probably by solution, from the amphi- 

 aster leaving the achromatic parts of the latter quite perfect (fig. 90) ; in other 

 cases, the achromatic part of the amphiaster as well as the chromosomes may be 

 undergoing solution (figs. 86, 91, 92). Figs. 91 and 92 show eggs in which the 

 position and the direction of the mitotic figures are abnormal. Finally, one 

 frequently finds eggs like fig. 93, in which the micromeres no longer form a flat 

 plate of cells covering over the macromeres, but rounded and irregularly scattered 

 cells. Such conditions, which are probably the same as those named framboisia 

 by Roux, are not limited to eggs treated with the electric current but may be 

 found in almost all cases of abnormality appearing in the later cleavage and 

 they probably represent the rounding up and separation of micromeres which 

 were formed normaUy. 



The abnormalities shown in Plates XLVIII and XLIX represent the principal 

 types of abnormalities found among eggs which have been subjected to the electric 



