376 Literarisch-kritische Rundschati. 



Now pbysiological response is not proportional to the physical 

 value of the Stimulus, but according to the Fechn er-Weber 

 Statement (which is probably a simplification of the facts) it 

 increases arithmetically as the Stimulus increases geometrically. 

 Moreover Geigel ignores altogether the consideration of the 

 " threshold value " (Schwelle n w e r t) of a Stimulus, below 

 which minimum no response is evoked: "de minimis non curat 

 lex" viventium. According to Geigel the blunt elongated finger- 

 shaped pseudopods of many Lobose Ehizopods are impossible: it 

 does seem such a pity that Geigel's interest in biological questions 

 lias not so far induced him to study them for himself. We feel 

 this regret again, vvhen he discusses the chemiotaxy of the sperms, 

 in ignorance of the researches of H. S. Jennin gs,^) wlio has 

 shown so conclusively that most if not all cases of chemiotaxy 

 are better expressed in terms of negative preferential avoidance 

 than of positive preferential approach. Thus Paramecium 

 moving in water rieh in CO2 swim about indifferently so long as 

 it is in this favoured region, but as soon as it passes away 

 from it, it stops, reverses, turns and change sits direction of 

 progress. As the sperms spread evenly in the medium we must 

 suppose that they avoid one another. There is no need to postulate 

 with Geigel a new physical force at work in the approach of 

 the sperm to the oosphere, and the formation of the receptive 

 hillock on the latter. 



Conclusions. 



(1) Geigel's contention that in a field of centred force 

 the axial chromosomes in discession should lead while 

 the peripheral ones lag is correct. 



(2) This characterises the behaviour of actual chromosomes 

 during anaphase. 



(3) His belief that this is not the case in the living cell 

 is contrary to observed facts, and is based on an inadequate 

 knowledge of the subject, and reliance on misleading 

 diagrammatised figures. 



(4) The scarcity of anaphases in fixed specimens is probably 

 due to the speeding up of the chromosomes as they 

 approach the poles: — it is a fact that teils in favour 

 of centred-force hypotheses, 



1) Contributions to the study of Behavior in the Lower Organisms. 



