282 BULLETIN OF THE 



Flemming erroneously concluded that the centres of the peculiar radial 

 arrangements of the cell protoplasm were probably to be considered as 

 formative centres (Bildungscentren) for the new nuclei, and asserts that 

 the segmentation cells of the Anodonta germ actually pass through 

 stages in which they are without nuclei."^ 



While Fol and Biitschli agree in the interpretation of the radiate phe- 

 nomenon as being the result of an attractive force, chey are diametrically 

 opposed on the old and cardinal question of the persistence or disappear- 

 ance of the nucleus. While Schneider and Biitschli are in agreement on 

 this point, Flemming's testimony is all in favor of the non-persistence of 

 the nucleus. The last-mentioned observer justly makes prominent the 

 fact, that the arrangement of the yolk granules is dependent on the con- 

 dition of the clear protoplasm, — the star proper. 



Since the appearance of these four papers much attention has been 

 given to the phenomena which they discuss. 



Whitman {'78", p. 16) cites Metschnikofp (74) as having seen and 

 described the radiate structure in Geryonia (p. 19) and Polyxenia. As 

 regards the entoderm cells of Geryonia (Taf II. Fig. 7. B), I doubt if 

 the structure has anything to do with the molecular asters developed 

 at the time of segmentation. Metschnikoflf himself speaks of these irreg- 

 ular fleecy-looking stretches of protoplasm as the " die bekannten Pro- 

 toplasm aauslaufer," which would hardly be the expression to be used 

 of molecular asters. It is in reality a permanent phenomenon, (if one 

 may speak of anything as permanent in a growing organism,) which is 

 most prominent in the least active period of the individual cell's exist- 

 ence. In the segmentation spheres of Polyxenia before the differentia- 

 tion of ectoderm and entoderm (Taf III. Fig. 3), it may reasonably be 

 claimed that the rays figured are due to the same influence as those 

 which induce the molecular stars ; but the figure, after all, is hardly more 

 suggestive of the real aster with its multitudinous rays than are Grube's 

 drawings in the case of Clepsine. I do not find that Metschnikoff makes 

 any explanation of this figure in the text. 



* The radical tone of this statement is considerably modified by the very re- 

 strictive definition which the author formulates for "nucleus." "DerNameKem 

 kniipft sich fiir uns einstweilen an bestiramte Merkmale : eine Membran oder eine 

 scharfe Absetzung nach Aussen, einen von der Umgebung verschiedenen Inhalt und 

 meistens einen Kernkorper." "Die Substanz des nicht mehr sichtbaren Nucleus 

 wird jedenfalls in irgend einer Form in den Zellen noch vorhanden, vielleicht sogar 

 localisirt sein ; aber wer sie in diesem Zustand Kern nennen wollte, der wiirde mit 

 gleichem Recht die Auflbsung eines Kochsalzkrystalles als einen Krystall bezeichnen 

 kbnuen." (!) 



