THE GENEKA AND SPECIES OP SYMPHYLA. 7 



same leg and the same claws in the same position in order to 

 facilitate a direct comparison of the shape, etc., of the parts 

 in question. Furthermore, the legs of the last pair, the legs 

 of the first pair if these are not quite rudimentary, and the 

 cerci have always been drawn with the same degree of 

 enlargement, the claws of the first and the last pairs of legs 

 with a higher degree, which is identical for both figures; the 

 result of these arrangements is that the figures also show the 

 proportions as to length, etc., between the cerci and the legs 

 mentioned of each species, (Of course, it has been impossible 

 to draw the legs and cerci of a small and of a large species 

 with the same degree of enlargement, for the figures of the 

 large species would be enormous if those of the small one 

 should be really useful and not too small.) I should advise 

 future students of this order — and of many other groups — to 

 follow a similar plan when drawing figures. 



III. On some Structural Features and Characters. 



A. Variation. — It may be practical to begin with some 

 remarks on this topic. During a preliminary study I was 

 induced to think that it would be rather ea.sy to separate and 

 describe nearly all the species of the genus Scutigerella, as 

 they presented several characters, whereas the other genus, 

 Scolopendrella, seemed to be more difficult; but later on I 

 arrived at the opposite result. The species of the last-named 

 genus show several characters, and most of the features which 

 differ from each other in all or nearly all species present onl}^ 

 a slight or no variation in specimens with the full number of 

 legs of the same species. In Scutigerella, at least, several 

 species show a special difficulty : specimens of the same species 

 having acquired the fidl number of legs vary very much in 

 size; this difference can be very large between specimens 

 from the same locality or from different localities, and arises 

 often, most probably, from the age of the individuals ; but 

 sometimes it is a real local variation, a remark already set 



