:36 THE SCOTTISH NATURALIST 



SCOTTISH HAIRWORMS {NEMA TOMORPHA, 

 GORDIIDyE), THEIR OCCURRENCE, HABITS, 

 AND CHARACTERISTICS; WITH A KEY 

 FOR THE DISCRIMINATION OF THE 

 SPECIES RECORDED FROM BRITAIN. 



By James Ritchie, M.A., D.Sc, The Royal Scottish Museum. 



{Continued from page 115.) 



(b) Diagnostic Characters. — In addition to the above 

 characters there are some which on account of their constancy 

 in groups or in individuals are of special value in separating 

 Hairworms into genera and species. 



i. The hinder end. In all the species so far recorded from 

 Britain the hinder end differs in male and female specimens. 

 In the females it is simply bluntly rounded except in 

 Parachordodes tolosatius, and with this exception offers no 

 diagnostic character. In such cases recourse must be had 

 to skin characteristics. In male examples the hinder end 

 is forked, two rounded branches being separated by a deep 

 slit or embayment, near the inner angle of which lies the 

 cloacal opening. This fork affords diagnostic characters of 

 great value, owing to the presence in its neighbourhood of 

 series of minute bristles or of thickened folds of skin 

 arranged in varied patterns. 



ii. The skin or cuticle. As important as the forked hinder 

 end are the characters afforded by the skin. This may be 

 smooth or mapped out in more or less regular patterns, which 

 unfortunately are often so delicate and fine in structure that 

 they can be satisfactorily determined only by the use of high 

 microscope magnifications. There are three grades of such 

 markings : an exceedingly fine diagonal meshwork resem- 

 bling on a delicate scale the " stipple " of a half-tone process 

 block ; a series of larger patterns of varying design— circles, 

 " areoles," meshes, etc. ; and distinct protuberances or papillae, 

 sometimes with associated hair-like growths. 



(c) Mode of Preservation and Examination. — Owing to 



