A CONTRIBUTION TO THE BIONOMICS 

 OF ENGLISH OLIGOCHyETA 



PART II.— BRITISH ENCHYTRAEIDS: THE ROLE 

 OF PACHYDRILUS 1 



By the Rev. HILDERIC FRIEND 



Enchytrceids with Red Blood. — Among the many genera which 

 go to make up that family of Oligochaets or Annelids which is 

 known as the Enchytraeidae there are two in particular which 

 are characterised by the possession of red blood. These are 

 at present known among zoologists as Lumbricillus and 

 Marionina ; but for some time they were better known as 

 Pachydrilus — a name which was first applied to the genus in 

 1861 by Claparede (1). Since the colour of the blood seems 

 to bear a distinct relationship to their habitat and economy 

 they may be regarded as forming a group by themselves, and 

 this group it is convenient to designate the Pachydrilid section 

 of Enchytraeids. While the rest of the Enchytraeidae have, 

 with very few exceptions, colourless blood, and as a rule lead 

 a terrestrial life, the Pachydrilids with their coloured blood 

 are either purely aquatic or show a decided preference for very 

 moist localities. If we may state the facts in another way, 

 the red-blooded Enchytraeids are aquatic with weak terrestrial 

 tendencies, while the white-blooded genera are terrestrial with 

 but weak aquatic tendencies. 



I have, it is true, occasionally found Pachydrilids in garden 

 soil, but their presence in cultivated ground is always regarded 

 as an unusual fact. At the same time Enchytraeids with 

 colourless blood are much more frequentfy found leading a 

 semi-aquatic life, and a few species belonging to this group 

 prefer such conditions to a purely terrestrial existence. It 

 will, however, be obvious to the careful observer that the two 



1 See Science Progress, No. 29, July 1913, vol. viii. pp. 99 et seq. y for the first 

 part of our study. 



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