1 894] 



THE BRITISH NATURALIST. 



49 



0. helopioides very sparingly. Perhaps I should take more if I knew the 

 most likely spots to search. As a rule I find it at roots of trees near the 

 water, or hibernating in rotten stumps." Several localities are given in 

 Fowler's " Coleoptera of British Isles." Ireland: The Rev. W. F.Johnson 

 writes that Oodes helopioides " has no record from Ireland ; there is a 

 specimen in the collection of the Belfast Museum, but, as it is without 

 label, it is probably not a native." 



AIR-BREATHING ARTHROPODS. 



BY LINNAEUS GREENING, F.L.S. 



( Continued from page 15.^ 



For instance, the majority of them possess a pair ot sense organs on 

 the head, the antennae, but these are wanting in the Arachnida; again, 

 most insects are winged, but it is of course well-known to every 

 entomologist that there are exceptions to this rule. 



There is little room to doubt that all the Arthropoda have developed from 

 worm-like ancestors ; and in very early times these branched off into two 

 main lines, the Crustaceans on the one hand, and the Tracheata on the 

 other. The tracheal system is unquestionably a modification of that 

 water-vascular system present in many worms ; and although the 

 worm-like ancestors of our air-breathing Arthropods were, in the far-off 

 past, aquatic, there is no doubt that the earliest true tracheal system 

 occurred in one of their terrestrial descendants, which in some other 

 respects resembled our modern Peripatus. The but slightly modified 

 descendants of this earliest tracheate form constitute the lowest of the 

 five classes of our air-breathing Arthropods. This class, Onychophora, 

 embraces but genus Peripatus, which has about 14 species; all are 

 small animals and may not unreasonably be described as annelid worms, 

 plus a pair of antennae, a pair of segmented legs on each body ring, and 

 a tracheal system of breathing. Like most archaic forms they are 

 widely distributed but relatively few in number, and they are the lonely 

 representatives of a race which was once the summit of the animal 

 kingdom ! Following closely upon the heels of this primitive Peripatus 

 •came the earliest representative of the second class, the Myriapoda. 

 These animals are Peripatus, plus a harder and stronger exo-skeleton, a 

 body and limbs presenting more definite segmentation and showing 

 traces of the tendency, so much more pronounced in the higher classes, 

 of some of the somites, to coalesce. This tendency is especially marked 

 in the Chilognatha, the majority of whose body segments bear two pairs 

 of legs, clearly indicating that each segment represents two coalesced 

 somites, or body rings of the ancestral form. 



