WATEK-SPIDBKS AND WATEE-WOKMS. 283 



because in feeding upon dead animal matter they perform the 

 dntieB of excellent scavengers. They are able, in common 

 ■with some of the univalves, to support themselves in the water 

 by what may be called a mucous thread. These creatures 

 are oviparous, but the young remain affixed to their parent's 

 body for some time after they are hatched. Planarian Worms 

 will live for a long time in the aquarium, where I have never 

 known them do any harm. They will sometimes, however, 

 attack a diseased fish. The largest of these animals is, 

 perhaps, P. laetea, which will sometimes, when well extended, 

 measTire nearly lin. in length. The Planariae, on being 

 touched, either contract and harden themselves, or let go 

 of that to which they are clinging and sink in the water. 

 They progress by glidiag evenly over the stones, weeds, or 

 mud. 



