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2. Cytasters and Centrosomes in Artificial Parthenogenesis. 



By Edmund B. Wilson. 



eingeg. 4. Juni 1904. 



In a recent paper on artificial parthenogenesis by Dr. A. Pe- 

 trunkewitsch^ doubt is cast upon my results regarding the origin 

 of the centrosomes in artificially induced parthenogenesis in sea- 

 urchins, an endeavour being made to show that the centrosomes of the 

 multiple asters arise, not by new-formation as I concluded, but by 

 progressive division from the primary egg-center. This result has 

 been based on an evidently conscientious research, and is supported 

 by figures that may seem convincing to those who are not sufficiently 

 familiar with the object or not fully acquainted with the evidence. 

 The importance of the question at issue leads me therefore to point 

 out on how inadequate, and in some respects misleading, a basis the 

 conclusions of Dr. Petrunkewitsch rest. 



The author seeks to establish the conclusion that those asters 

 which contain central bodies (»echte Strahlungen«) are of wholly 

 different nature from the smaller ones that do not contain such bodies 

 (to which alone he would apply the term 'cytasters"), and finds that the 

 former arise only by progressive division from the primary egg-center, 

 and do not form at all in enucleated egg-fragments — » daß eine Neu- 

 bildung von Centrosomen nie stattfindet, daß vielmehr allen neuge- 

 bildeten echten Strahlungen als Zentren echte Centrosomen dienen, 

 die durch die Theilung des Eicentrosomas entstanden sind« (S. 35). 

 In preparations, »können wir die ganze Entwicklung der Strah- 

 lungen Schritt für Schritt verfolgen, wir können die Entstehung der 

 Centrosomen aus dem Eizentrum nachweisen« usw. (op. cit. S. 37). But 

 the series of figures (Figs. 15 — 20), given in support of this rather 

 sweeping assertion, afi"ords no real basis for such a conclusion, and in 

 the light of my observations on the living eggs is open to an entirely 

 different interpretation. This series of figures is in fact constructed 

 by the selection of preparations of fixed material; and that they 

 represent successive stages of development is quite arbitrarily assumed, 

 without the least evidence that such is the case. Readers of my paper 2 

 will recall that definite evidence was there given to the contrary. 

 Especial emphasis was laid on the fact that in the transparent living 

 eggs of Toxopneustes, where the division of the cytasters can really 

 be followed »Schritt für Schritt«, the asters are seen forming simul- 



1 Künstliche Parthenogenese, in Zool. Jahrb., Supplement, VII, Weismann 

 Festschrift. 



2 Arch, für Entwicklungsmechanik, XII, 4 (vgl. S. 542, 578 usw.). 



