26o THE SCOTTISH NATURALIST 



Of microscopic characters^ the most readily distinguished of 

 those common to both male and female specimens is the smoothness 

 of the cuticle and the entire absence of the raised tubercles or 

 areolar formation which occur in all other British species. There 

 are present, indeed, the very fine crossed lines common to all species, 

 and due to fibrils underlying the cuticular surface, and amongst 

 these larger regularly rhombic areas may be marked off. In some 

 specimens also a semblance of a hexagonal areolar formation may 

 occur, but these polygonal formations are very obscure, and seem to 

 be in no way due to definite thickenings of the cuticle itself, as 

 in true areolar formation. The point can readily be tested by 

 microscopic examination of the profile of a longitudinal section ; 

 for whereas in other species the profile is ornamented by regular 

 mounds and hollows, or by distinct tubercles (see Fig. 4), in 

 G. villoti it is quite smooth and flat. At various times distinct 

 species have been created for the areolate forms (e.g. Gordius 

 tatre?isis, Janda), but the consensus of opinion is that they simply 

 represent varieties of G. villoti. In the Scottish specimens close 

 examination with high magnifications has generally revealed the 

 small polygonal pattern, but even in a single batch of specimens 

 taken from the same locality at the same time, the variation as 

 regards distinctness is extreme. 



Male specimens afford additional diagnostic characters. Their 

 bodies are distinctly more slender than those of females, 0.4 mm. 

 as compared with 0.6 mm., and the hinder end is bifurcated. The 

 arrangement of structures in the neighbourhood of the fork are of 

 specific and even generic significance, for in Gordius alone is there 

 present between the cloacal opening and the axil of the fork a 

 strong, prominent ledge of chitin, horny brown in colour (see Fig. 6). 

 In G. villoii\h.\s post-cloacal ridge is in the form of a rounded arch 

 or horse-shoe, the inner side of the arch bending round the axil of 

 the fork and away from the cloacal opening. The branches of the 

 fork are flattened on the inner sides for part of their length, the 

 margin of the flattening being marked by a row of minute scattered 

 tubercles, and very short, hair-like processes stretching from each 

 end of the post-cloacal arch to the side of the branch. The margin 

 of the cloacal opening has none of the ornamentation due to cuti- 

 cular thickenings that is observable in Parachordodes violaceiis. 



Distribution. — The species is common in the palaiarctic region. 



British Isles. — Gordius villoti has not hitherto been recorded, 

 as such, from Great Britain, though Camerano has recently identified 

 a number of Irish specimens. It is possible that some of the 



