654 MR JAMES MURRAY ON 



E. muscicola, Plate? (13). (Plate I. fig. 6a, 66.) 



Description. — Small, red ; plates 10, arrangement normal, 3 median ; granules coarse, 

 regular. Lateral processes 4 on each side, all setse [a, c, d, e). Dorsal processes, 

 one strong spine on each plate of first pair. Fringe on fourth legs. Strong barbs on 

 claws. 



Length 185m (excluding the legs). Eggs large, (5 8m), nearly round, red. 



Monument Hill, Comrie, Perthshire, June 1905. 



The number of processes corresponds with that of E. testude and E. muscicola, but 

 their position differs from both. As the dorsal spine is over seta c, the correspondence 

 is closest with B. muscicola, Plate, but the lateral setae of that species are a, b, c, d. 



Genus Macrobiotus. 



It has been thought that most of the organs which might have been used in dis- 

 criminating species were too variable to permit of their use in this way, the claws alone 

 being regarded as trustworthy characters. In consequence of this supposition most 

 of the earlier species are insufficiently described, and are hardly recognisable ; they can 

 only be firmly established by subsequent more detailed diagnoses. 



With increasing experience, faith is being established in the practical constancy of 

 most of the structures, or at any rate it is now supposed that their variability is con- 

 fined within narrow limits. If further work confirms this belief, it will have to be 

 conceded that species are much more numerous than has hitherto been supposed. 



An amount of caution in describing new species is laudable, yet too much of it 

 may hinder the progress of knowledge. 



The most different animals have been regarded by various observers as M. hufelandi, 

 partly because they allowed too much for variation, and partly because they supposed 

 there were only a few species in the genus, whereas there may be probably from 12 to 

 20 or upwards of common species in any district. 



Lance (4) naively (p. 206) discusses the improbability of the existence of M. tuber- 

 culatus, Plate, merely because he hadn't found it. 



The three most useful characters in framing diagnoses are, the pharynx, the claws, 

 and the egg. Of secondary but still great importance are the teeth and the texture 

 of the skin. 



The pharynx. — The chitinous rods in the pharynx are found in three principal 

 types. There appears to be nearly always a short, thick process attached to the end 

 of the gullet. The differences of the three types are found in the succeeding 

 thickenings. 



The hufelandi type of pharnyx has in each row of thickenings two unequal rods, 

 the first, nearest the gullet, longer, and apparently formed by the junction of two shorter 

 rods ; the second usually about half the length of the first. The second type, which 



