Ortmann.] * lo4: [May 15^ 



and if we see the same variation present in different degrees in a large 

 number of individuals, we have reason to suppose that inheritance plays 

 a part, since the amount of change, if often inherited, must on the one 

 hand increase, and since, on the other hand, the force of inheritance is 

 generally different in each individual. Thus orthogenesis, variation in a 

 distinct direction, is the result of the combined action of variation and inher- 

 itance : but it is "perhaps advantageous to accept Eimer's term, because, 

 as we have seen above, it is important as regards the transformation of 

 species. 



Orthogenesis results in series of variations consisting each of a number 

 of individuals varying in the same direction but in a different degree : it 

 unites the single variations into varieties, that is to say, into groups of 

 animals showing the same tendency of variation. This grouping of vari- 

 ations into varieties is especially due to inheritance. 



Eimer tries farther to find out the causes of the breaking up of any 

 series of variations into species, and reaches the conclusion that species 

 are formed when a certain group of individuals within a series "loses its 

 connection with its other allies."* This breaking up of a series of varia- 

 tions in consequence of lost connection he calls " genepistasis."^ Under 

 this head come, according to him, Oeograpliical Separation, Ilalviatogcn- 

 esis, and Kyesamechaina.X 



If we direct our attention to the general definition of " genepistasis" 

 given by him, that it is the losing of connection of certain groups, we see 

 at once that genepistasis is exactly the same as separation, and under 

 the same head comes kyesamechania.^. The latter term means that a 

 sexual crossing between animals of more or less different characters is 

 rendered impossible by morphological or physiological causes. This im- 

 possibility of crossing is certainly not the first cause of difference, but it 

 is the result of already existing differences produced by beginning separa- 

 tion, and as respects the formation of species, kyesamechania can never 

 be a primary cause of the origin of different species, but it is the result of 

 the beginning differentiation, and may develop an additional factor accel- 

 erating the process of specific differentiation. 



As regards Balmatogenesis, which means the sudden appearance of any 

 new variation, Eimer explains this process by correlation :| but this 

 explanation is insufficient. If any character changes, other characters 

 connected by correlation with it change also, but if the change of the first 

 is slow, certainly the changes of the others are so also, and a sudden 

 change of characters by correlation presumes a sudden change of the 

 leading character. Tlius correlation cannot explain balmatogenesis. 



*SeeZ. c, p. 26 : " Wenn .... eiue Gruppe von Individuen .... auf irgend eiue Weise 

 die Verbindung iiiit den iibrigen Verwandten verloreu liat .... spriLlit uiun von Arton." 



fSee /. c, p. 30ff. 



1 1 cannot make out with certainty what Einipr thinks as to tlic logical relations of these 

 terms to each other, hut I hope I have quoted him correctly. 



g See Eimer, Die Artbildung und Venvandtschaft bei den Schmetterlingen, ii, 1895, p. 14ft". 



II See Enlslehung, etc., p. 5:i. 



