34 EARTHWORMS AND THEIR ALLIES [ch. 



may be also mentioned that among the aquatic 

 families as a rule the intersegmental septa do not 

 show that thickening in some of the anterior segments 

 of the body which is so general a feature of the land- 

 dwelling species. Finally it is only among the aquatic 

 forms, and among them only in the families Aeolo- 

 somatidae and Naididae, that asexual reproduction 

 by budding takes place. Indeed so common and 

 usual is it in the genera of these families that even 

 yet there are considerable lacunae in our knowledge 

 of the organs of reproduction in the said families. 



Together with these general similarities are many 

 points of structural difference among the worms 

 inhabiting ponds, lakes, and rivers, which allow of 

 their being divided into a number of quite distinct 

 families. 



One of the most distinct of these families and 

 lying in any case quite at the base of the series is 

 the family Aeolosomatidae which includes a number 

 of distinct species of delicate and transparent 

 worms, and in whose integument are embedded 

 round cells bearing a large brightly coloured oil drop ; 

 this is reddish or green in colour, or and this more 

 rarely colourless, but still recognisable as an oil drop. 

 The green sometimes even verges upon blue on the 

 one side and yellow on the other, while the red may 

 approach brown or purple. These worms are assigned 

 for the most part to the genus Aeolosoma which is 



