Allgemeine Biologie und Entwickelungslehre. 17 



Variabilitat der Anfang zur Auflosung der Species in mehrere ist. Die do- 

 mesticirten Rasseii sind keine Artenanfange, sondern gehoren in die Categoric 

 des individuellen Polymorphismus. Hierher auch oben Arthropoda p 68 



Petersen( 2 ) und Vertebrata p 196 Balducci. 



Nacli Plate (^ besteht kein principieller Gegensatz zwiscben Variationen und 

 Mutation en. Zu unterscbeiden sind 3 Gruppen von Variationen: die nicbt 

 erblichen rein soniatiscben Abanderungen oder Somationen, die Fluctuationen 

 mit einer Erbziffer bis zu 50^ und die noch starker vererbbaren Mutationen. 

 Die F. zeigen in der Regel Ubergange und geriuge correlative Verkettung, 

 wahrend die M. obne Ubergange, aber als Gruppenauderungen auftreten . 

 Im Laufe von Generationen konuen die F. zu M. werden; Verf. zahlt die fur 

 diese Moglichkeit sprechenden Facten auf. Die Mutationslebre vermag das 

 Auftreten neuer Arteu uud die allmahliche Anderung der Formen nicht ver- 

 standlich zu machen, deun die Mut. sind (nach De Vries) richtungs- uud 

 regellos, ferner bei ihrem Auftreten aufierst selten und gestatten nicht die 

 Ableitung von Airpassungen. - - Hierher auch oben Coelenterata p 15 Hargitt( 2 j, 

 Mollusca p 17 Davenport uud Tunicata p 3 Conklinf 1 ). 



Uber Vererbuug s. Andriezen, Burbank, Castle(>- 3 , 5 ), Cockerell, Conklin, 

 C. Crampton, H. Crampton, Doncaster, Dwight, Halsted, Hink, Kraemer. 

 Kranichfeld, Loisel( 3 ), Loomis, Morgan! 1 ), Punnet^ 1 ), Ross, Sandsten, Tsche- 

 pourkowsky, Webber, Wheeler, Woods, Zieglerl 1 , 2 ), sowie oben Coelen- 

 terata p 1 Morgan ( 2 ) und Ecbinoderma p 5 Godlewski; iiber Vererbung er- 

 worbener Eigenschaften De Meyer, Kassowitz und Poulton; ftber Telegonie 

 Dilbois, Loisel( 2 ) uud obeu Arthropoda p 70 Sitowski( 2 ). 



Bateson gives a summary of the chief results which have been obtained on 

 Mendelian inheritance, together with a brief outline of the possible bearing 

 of these results ou general problems of variation, evolution etc. He "is con- 

 vinced that the investigation of heredity by experimental methods offers the 

 sole chance of progress with the fundamental problems of evolution". He 

 inclines strongly to the view that sex will be found to be a phenomenon of 

 Mendelian segregation. A number of real or apparent exceptions to Mendel's 

 laws are discussed. 



Darbishire gives a general discussion of the relation of Mendelian to 

 biometric interpretations of the results of investigations on inheritance, and 

 comes to the conclusion that the two interpretations are not incompatible. He 

 reexamines his own results on Mus and finds that the apparently conclusive 

 fact established by these experiments, that the number of albinos produced by 

 a given cross is influenced by the ancestry of the parents, is possibly capable 

 of Mendelian explanation. The suggested explanation turns on the fact that 

 a certain type of hybrids cannot be distinguished from pure dominants .except 

 by examination of their progeny. By the inclusion of these supposed hybrids 

 but really dominant individuals in one group of matings, the number of albinos 

 from those matings was brought below Mendelian expectation. It now appears 

 that the manner in which the Galtonian theory is also borne out by the same 

 facts "is by the gradual invasion of the 'hybrid' ranks in successive generations 

 by dominant individuals bearing the external hybrid characteristics". 



De Vries discusses the relation between the "sporting of inconstant varieties" 

 and true mutation. He considers that such varieties offer specially favorable 

 material for studying the laws of variation. 



Pearson ( 4 ) contributes a historical and critical discussion of the mathematical 

 theory of symmetrical and skew variation, bringing out many important points. 



