440 



WORMS. 



although it is capable of stretching itself much further, and its width is about 

 equal to that of a man's finger. On account of their burrowing habits, worms 

 are not very frequently seen, although periodically but only after heavy rains 

 they come to the surface of the soil in some numbers. Allied to the earth-worms 

 is the rare and extremely slender Phreoryctes menkeanus, which lives from 

 preference in wells and shallow water, in which it may be found in the greatest 

 abundance in May and June, disappearing in the winter. Another aquatic 

 member of the group is Tubifex rivulorum, a small red, translucent little worm, 

 found abundantly on the slimy bottoms of ditches and brooks. These creatures 

 remain with the forepart of the body stuck in the slirne, while the hinder end 

 keeps up a continual vibrating movement. Usually they are so closely packed 

 that the surface of the mud appears to be red coloured, and when startled, the 

 whole throng disappears like a flash into the slime. The clear transparent naids 

 behave in quite a different manner. These animals are also found in ponds 



and ditches, where they 

 may be seen winding 

 themselves in and out 

 amongst the stems of 

 duck-weed. One of the 

 best known is the beaked 

 nais (Nais proboscidea), 

 so called from a feeler- 

 like prolongation of the 

 head, which is furnished 

 with two conspicuous 

 eyes. These worms 

 frequently reproduce 

 spontaneously by fission, 

 and it is not uncommon 

 to see one individual in 

 process of giving rise 

 to several others. 

 Amongst the bristle- 

 worms is placed the 

 family Myzostomatidce, 

 which was long a puzzle 

 to zoologists. The species 



are all of small size, the largest, Myzostomca gigas, measuring only a little more 

 than a quarter of an inch in length. The body is short and oval. Its upper 

 side, which is variously coloured, is covered with fine threads, called cilia, and its 

 edges are prolonged into ten pairs of long, slender, flexible appendages, while 

 below there are five pairs of horny tipped parapodia, and four pairs of cup-like 

 suckers. All the members of this anomalous family are parasitic upon stone- 

 lilies or crinoids, but the degrees of parasitism are various, some kinds wandering 

 freely about their hosts, while others cause those curious swellings which appear 

 upon the arms of the infested animal. 



BEAKED NAIS, Ndl 



idea (enlarged 10 times). 



