174 RALPH S. LILLIE. 



The preponderance of negatively charged ions at the surface 

 of the egg must result in a fall of surface-tension, and it is to this 

 that cleavage on the above theory is supposedly due. That 

 alterations of surface-tension do actually accompany a passage 

 of the chromatin into the chromatic phase, even when normal 

 cleavage fails to occur, seems proved by certain recent obser- 

 vations of E. B. Wilson 1 on artificially fertilized eggs of Tox r 

 opncustes. It was found that a limited number of eggs after 

 having been exposed to the action of the fertilizing solution 

 (mixture of equal parts sea water and 12 per cent, magnesium 

 chloride) do not segment (as do the majority of eggs thus 

 treated) but undergo the following abnormal changes : " the 

 nuclear area gives rise to a single radiation or monaster which 

 never resolves itself into a bipolar figure. Such eggs never 

 properly segment, but pass through regularly alternating phases 

 of nuclear transformation parallel to those of progressively divid- 

 ing eggs." That is, first the nucleus enters the resting phase and 

 the astral radiations become greatly reduced ; then the nuclear 

 membrane again disappears and the astral radiations regain their 

 original prominence ; this is again followed by the reconstruction 

 of the resting nucleus and the reduction of the radiations. The 



o 



above cycle of changes may occur several times in succession 

 in a single egg. At each disappearance of the nuclear mem- 

 brane a group of granules appears in the clear center of the 

 aster; these are believed to be chromosomes. These bodies pro- 

 gressively multiply by longitudinal division until finally they may 

 become very numerous. The important fact from our present 



An interesting incidental result of these conditions is a tendency for any minute 

 electrically negative particles casually present in the cytoplasm to be drawn along the 

 lines of force toward the regions of highest positive potential. Here such particles 

 must gather and remain, and in stained preparations they may present the appearance 

 of prominent deeply staining bodies occupying the astral centers. On the above the- 

 ory the centrosomes originate in some such manner as this. The affinity exhibited by 

 these bodies for basic or nuclear dyes may be regarded as additional evidence of their 

 acidity and electrical negativity. It should be remarked that other authors have re- 

 garded the centrosomes as formed by the aggregation of centripetally moving micro- 

 somes (cf. Biirger, Anatomischer Anzeiger, 1892, p. 222). On the above theory this 

 migration is due to electrical influences. Later, however, I hope to treat these and 

 related questions in a somewhat less summary manner. 



J Wilson, foe. cit., pp. 546, 547. 



