OBSERVATIONS ON CRIODRILUS LACUUM. 559 



degenerate. I have never been able to study the copulation, 

 though I have looked at many worms. The swellings, around 

 and in front of the male genital pore, are, however, so very 

 swollen during the breeding season, and secrete so much mucus, 

 that I presume the copulation takes place as in the Lumbri- 

 cinae. The worms found in the mud are very active, they 

 burrow deep into the mud; I have even met them at a clay 

 bottom, wherever the penetration of the water through the 

 deeper layers renders their passage possible. In very shallow 

 water, areas regularly and finely perforated are to be seen at 

 the sides and bottom of the channel, which disclose their 

 presence ; these perforated places can frequently be used as a 

 guide to their discovery. They only live scattered over a terri- 

 tory : as they can swim in a peculiar serpentine way they wander 

 to different places, and settle where the necessaries of their life 

 are present. Their food consists of rotting and decaying 

 vegetable matter, which they swallow mixed with mud. Their 

 size varies according to their habitat and local circumstances, 

 as the statements of other observers affirm. However, even 

 under the same circumstances, very great differences in size 

 exist, so that, I think, in the first place individuality, and in 

 the second place environment must be considered as factors 

 in their varying size. 



In the economy of nature they appear to do good service by 

 their destruction of organic matter ; their faeces, as in the case 

 of Earthworms in general, increases the goodness of the mud, as 

 is proved by the settlement of many plants in the places where 

 Criodrilus lives. The mud of such a bottom is very rich, and 

 on the overflowing of the stream it will be carried over the 

 fields where it is of further use for the nourishment of plants. 



In winter these worms burrow very deep in the mud, so that 

 one can dig them out only from very great depths. Their 

 tenacity of life is great, yet after this season they are very much 

 changed. In winter they soon perish in tanks with pure water, 

 but in autumn they can be kept for a week. In the tanks they 

 twine themselves into a knot and are then very difficult to 

 separate. Their power of regeneration is astonishing. A 



