48 EARTHWORMS AND THEIR ALLIES [ch. 



family Geoscolecidae as a whole which might be 

 regarded as fitting them for a purely aquatic life. 



Of this family one entire sub-family, the Criodri- 

 linae, is very nearly purely aquatic in habit. Two 

 genera, viz. Callidinlus and Glyphidrilus, out of 

 another sub-family, Microchaetinae, which contains 

 perhaps five other genera, are also aquatic in their 

 mode of life. In examining into the characters of 

 the various aquatic species with a view to searching 

 for common characters which might be put down to 

 modifications induced by the aquatic life, there are 

 two or three which arrest attention. In the first 

 place the Criodrilinae never possess a well- developed 

 gizzard, having at most a rudimentary gizzard, or 

 even two. However this character is not of universal 

 applicability, for both Callidrilus and Glyphidrilus 

 have got a gizzard and a strong one. These later 

 genera however have no calciferous glands or oeso- 

 phageal pouches of any description, structures which 

 are also absent among the Criodrilinae. It will be 

 remembered that the purely aquatic families, 

 Tubificidae, Lumbriculidae, etc., rarely show 

 signs of a gizzard and rarely possess oesophageal 

 pouches of any kind. In view of the fact that in 

 the case of a life in fresh water no calcareous salts 

 are necessary to resist the acids of the soil, and 

 that the mud passed through the alimentary canal 

 is already finely divided, it is not surprising to 



