AQUATIC EARTHWORMS 



63s 



Development of budding zones in Stylaria lacustris. 

 A, An early stage. B, A later stage. C, Still later stage with 

 a second budding zone well started. X2S. (After Leuckart.) 



gives rise to a definite number of new somites (five in most species 

 of Naididae), which form the anterior part of the posterior daughter- 

 worm. The daughter-worms, before separation, may in turn de- 

 velop budding zones, and in some cases even a third series of these 

 zones may appear and 

 thus give rise to chains 

 of incipient individuals, 

 or zooids. In some spe- 

 cies chains of eight zooids 

 are of ordinary occur- 

 rence. In the genus 

 Chaetogaster the plane 

 of division is in a septum 

 between two somites. 



Although many aquat- 

 ic OHgochaeta have the 

 power to regenerate 

 missing parts, greatly developed, there is lack of evidence that it is 

 of much importance in normal reproduction. 



Environmental Relations. The well-known investigations of 

 Darwin and others, on the action of terrestrial earthworms on the 

 soil and its organic contents, have led to a general appreciation of 

 the importance of the relations of these animals to their surround- 

 ings. It is less generally understood that their aquatic relatives 

 play a very important part in reducing the great masses of aquatic 

 vegetation to a finely-comminuted condition. OHgochaeta of 

 various species abound in the mud at the bottom and along the 

 shores of most bodies of fresh water, and an almost continuous 

 stream of this mud with its deca3dng organic contents is passing 

 through their bodies and being still further subdivided and de- 

 prived of organic material and its available energy. Niunerous 

 other species swarm in the decaying leaves and stems of coarse 

 vegetation of swampy areas and materially aid in their disintegra- 

 tion, while still other kinds populate the floating masses of algae, 

 which they rapidly devour as decay progresses. Since under 

 favorable conditions it requires but two or three days for Naidi- 

 fonri worms to reproduce by budding, they multiply with such 



