274 BULLETIN OF THE 



nuclei in a cell with undivided protoplasm has sometimes furnished the 

 basis for an inference that an actual division had taken place. Yet the 

 most accurate, connected, and careful of these observations failed to 

 disclose what improved means of investigation have shown to be of very 

 general occurrence. 



One thing, however, especially in the case of segmentation, had been 

 very often recognized in the best observations ; namely, that the nucleus 

 about to divide was a homogeneous body, exhibiting neither membrane 

 nor nucleolus, and often that its outline became quite indistinct. 



Among the papers which take notice of this interesting peculiarity 

 are the following. 



In 1846 the attention of Von Baer {'46, pp. 36, 37) was attracted by 

 the appearance of a " langgezogener heller Schein " in the eggs of Echi- 

 nus soon after fecundation, and also before each segmentation of the 

 yolk. At p. 39 he describes more in detail the condition of the mature 

 Qgg : " Im reifen Ei des Seeigels erkannte man an einer Stelle seiner 

 Oberflache einen hellen Kreis, der etwa ein Achtel vom Durchmesser 

 des ganzen Eies hatte. . . . Dass es nicht ein Blaschen oder eine Zelle, 

 sondern ein sehr weicher Korper ist, was ausserlich als heller Kreis 

 erscheint, glaube ich nach vielfaltigen Versuchen, die ich mit mechani- 

 schen Zertheilungen und einigen Reagentien anstellte, mit bestimmtheit 

 erkannt zu haben, obgleich dieser Korper bald in seiner Metamorphose 

 vollig durchsichtig wird." 



Lov^N ('48, p. 545), describing the development of Modiolaria and Car- 

 dium, says that " the nuclei of the cleavage spheres have no nucleoH, 

 and behave under the compressorium in no way like vesicles or cells. 

 They appear to be solid, but of quite limited consistence. Their peri- 

 odical disappearance can hardly escape observation, but it is more diffi- 

 cult to make out how this happens." 



As we have already seen, Warneck was certainly one of the first to 

 point out the peculiar modifications which the nucleus suff'ers before 

 its constriction and division. He was even impelled — probably in part 

 from the small size of the new nuclei when they first became visible as 

 distinctly outlined structures — to the conclusion that the nucleus un- 

 derwent actual diminution of volume during each act of division, without, 

 however, losing its identity. 



J. MiJLLER ('52% pp. 16, 17) speaks of "das Keimblaschen oder der 

 helle Kern^'' and states that it contains no germinative dot ; and in the 

 communication published in his Archiv ('52, pp. 11, 19) he expresses 

 even more clearly this peculiarity. "Das Keimblaschen im reifen Ei 



