Animon, Dei- Abiinderungsspielrauni. 311 



specimens and this affirmation is made, not empirically but after ex- 

 periment and endeavour. There are details that must have been lost 

 by the death, drying and staining- of the specimens, while the delicate 

 flow of sequences must have been lost. 



I daresay you may have noted that in my later papers I have 

 shown that the delicate use of a staining agent is. possible upon the 

 living form; it increases the death rate on the stage but it makes 

 some observations on the living organism easier. 



I venture then with deference to question whether the methods 

 employed by France are a fair test of the work done so long ago 

 on the ,,biflagellate" monad. May I not venture to ask you to con- 

 sider what appears to me to be the impossibility of finding on a 

 dried and stained specimen the spore -condition that is to say the 

 burst sac - shown in plates XXIV, XXVI, XLI, LXXXV and CIV, 

 amongst others of our joint papers. France is quite right when he 

 says that such observations are not (by his method) or are only with 

 great difficulty within the reach of our optical expedients. Even under 

 the very best conditions such apparatus must be of the very highest 

 quality, and employed by those who by long experience know how to 

 use them in such a way as to bring into operation their finest and 

 most perfectly corrected endowments. 



Of the accuracy of the joint observations of myself and colleague 

 upon the organism we have simply for the sake of our own conveni- 

 ence called the ,,biflagellate" I have not the remotest doubt. They 

 were not only made with great care and patience at the first, but 

 they have been more than once repeated and confirmed. But whether 

 it is identical with the Poly torn a of France's paper I do not venture 

 to decide. I do however, with all deference question the competence 

 and suitability of his methods as modes of criticism of the joint work 

 of Dr. Dry s dale and myself. [37] 



Very sincerely yours W. H. Dallinger. 



Otto Ammon, Der Abanderungsspielraum. 



Ein Beitrag zur Theorie der natiirlichen Auslese. Sonderabdruck aus: Natur- 

 wissensch. Wochenschrift. Berlin. F. Diimmler. 1896. 



Wer die Wirksamkeit des Selektionsprinzips auf die Umbildung 

 der Organismen anerkennt, muss zugleich zugeben, dass Aba'nderungen, 

 welche einen bestimmten Grad nicht tiberschreiten , fur das Gedeihen 

 ernes Lebewesens indifferent bleiben und deswegen von der Selektion 

 nicht beeinflusst werden. Es muss also einen ,,Abanderungsspiel- 

 raum" geben, innerhalb dessen Grenzen die Variation frei bleibt. 

 Werden nun die gemessenen Gro'Ben eines variablen Gegenstandes und 

 die Frequenzzahl jeder dieser GroCen in ein Koordinateu- System ein- 

 getragen, so dass die Abscissen den Grofien, die Ordinaten der Frequeuz- 

 zahl entspricht, dann ergibt sich daraus eine Kurve. 



