16 RANGE OF GENUS PERIPATUS. [CH. I 



distribution in a species of Tit. The Marsh tit, Parus 

 palustris, has a range nearly co-extensive with the 

 Palsearctic region; but it is known throughout this 

 immense tract of country in certainly three varieties. 

 One of these is found in Southern Europe, in Italy, 

 Turkey, Greece, and Asia Minor. The same variety does 

 not crop up in the intervening country but again appears 

 in South China. Whether this variety is entitled to 

 specific rank or not, the fact is remarkable and really of 

 equal value. It almost suggests an explanation that has 

 been sometimes advanced to account for discontinuous 

 distribution in the species of Mollusca. No great diffi- 

 culty could be felt in the assumption that the same 

 variety had been twice produced in localities of a somewhat 

 similar climate. Mr Wallace refers to one or two other 

 examples of a somewhat similar nature ; the Reed bunting 

 of this country reappears in Japan, being absent from 

 Asia. To take an instance from another class, Dr Scudder 

 records the existence of the butterfly (Eneis jutta 1 in the 

 Rocky Mountains of British Columbia and in Hudson's 

 Bay, and its absence from the intervening tract. 



The genus Peripatus* offers an example of a genus 

 with an exceedingly wide and at the same time discon- 

 tinuous distribution. Peripatus is universally regarded 

 as a very archaic form of Arthropod, which has preserved 

 certain characters of the worm-like ancestor from which it 

 is presumed that the Arthropods have been derived. 

 There are, for example, a series of paired excretory organs 



1 Butterflies of E. United States. 



2 Quart. Journ. Micr. Sci. vol. 28, 1888. 



