Ill] EXTERNAL FEATURES 59 



CHAPTER III 



THE EXTERNAL FEATURES OF EARTHWORMS AND 

 THEIR RELATION TO HABIT AND ENVIRONMENT 



To the very inexperienced eye all earthworms 

 might appear to be quite similar in detail as they 

 undoubtedly are in general form. But it needs not 

 a great deal of examination to detect even salient 

 characteristics whereby one kind may be distinguished 

 from another; to the expert it is possible in very 

 many cases to go no further than the outside before 

 assigning its correct place in the system to a given 

 example. The general external features of this group 

 of worms have been already dealt with in another 

 chapter. To some of these we again direct attention 

 in a more elaborate fashion in order to emphasise the 

 possible meanings of the variations met with apart 

 from their use in systematic arrangement. It is 

 difficult to say in comparing one worm with another 

 what is the most salient external difference. There 

 are however a few which may be regarded as equally 

 conspicuous on a nearer examination of the specimens. 

 The varying position and greater or less extent of 

 the clitellum, the longer or shorter retractile or non- 

 retractile prostomium, the position of the usually 

 conspicuous male pores, and the^existence of in the 



