184 THE ENTOMOLOGIST. 



SOME THOUGHTS SUGGESTED BY MR. HA.RCOURT- 

 BATH'S PAPER. {Ante, pp. 157-161). 



By J. W. TuTT, F.E.S. 



I HAVE tried to understand the various papers by Mr. Har- 

 court-Bath that have been published in the ' Entomologist ' 

 during the past twelve months, and have signally failed. I do 

 not wish to suggest this is Mr. Bath's fault, and I am inclined 

 to think it is rather my misfortune than my fault. There must 

 be, however, many entomologists in the same unfortunate posi- 

 tion as myself, and if this communication only serves to draw 

 from Mr. Bath an explanation more suitable to our meaner 

 intellects it will have fulfilled its purpose. 



Mr. Bath (ante, p. 158) makes the statement that " the 

 geographical and vertical distribution of the Rhopalocera, in a 

 very great degree, is so intimately connected with the distri- 

 bution of their pabula that it is reasonable to suppose they have 

 closely followed the various migrations of the flora upon which 

 they are so dependent both antecedent to and after the termina- 

 tion of the glacial period." To illustrate this he goes on : — " As 

 the genus Krchia is the most extensive and typical group among 

 the alpine butterflies, it will serve to illustrate with a certain 

 degree of accuracy the facts relating to the whole." Now the 

 pabula of the larvse of this genus is grass, and the species of 

 Erehia are not very particular as to the species of grass. Grass, 

 in great variety, extends from pole to pole. It is necessary 

 therefore, so far as I understand Mr. Batb, to get a knowledge 

 of the distribution of grass to obtain a knowledge of the dis- 

 tribution of the genus Erehia. Grass is found almost every- 

 where ; the species of Erehia are often extremely localised. 

 Their distribution is, of all genera, entirely independent of 

 the general distribution of their food-plant, and most of the 

 various species are often conflned to a certain small portion of 

 a valley in which tlie flora is practically identical over thousands 

 of acres. 



Having surveyed in the most cursory manner the distribution 

 of the genus in Europe, Asia, and North America, he concludes 

 that the species are segregated mainly in the Pyrenees, Alps of 

 Europe, Caucasus, Thiau Shan, Altai, and Amur. This is, of 

 course, such a well-known fact that it appeared to be hardly 

 worth mentioning. He also states that the species are very 

 scarce south of the mountain chains, and that this furnishes us 

 with an approximate estimate of the extreme distance south to 

 which the alpine fauna was driven during the climax of the 

 glacial period in the Palsearctic Region. 



Mr. Bath {ante, p. 159) sa3'8 that, " In preglacial times these 



