FRESH-WATER ANIMALS 89 



discussed. Furthermore, this single egg has a 

 special protective capsule formed around it, and the 

 young at the time of hatching has the form of the 

 parent and adopts at once its mode of life. 



Although jelly-fish, which are weak swimmers, 

 are apparently altogether unsuited to fresh-water 

 life, yet it is of interest to note that one truly fresh- 

 water form, Limnocodium, is known, while several 

 others occur in brackish water.* Limnocodium has 

 however only been found as yet in ponds, not in 

 streams, and the mode of its development is not 

 known. It was discovered a few years ago in 

 large numbers in an artificially heated pond of the 

 Regent's Park Botanical Gardens, and may possibly 

 have been introduced with the Victoria regia or 

 other plants living in the pond. 



Concerning " worms," few worms are more 

 familiar to microscopists than the Rotifers ; active 

 little animals, sometimes swimming freely, some- 

 times attached and living in tubes, and sometimes 

 massed together into colonies. Nothing is more 

 remarkable concerning them than their extraordinary 

 power of resisting desiccation. Mr. Sykes has 

 recently sent me some dust he collected more than 

 a year ago from a gutter on a house-top, and con- 

 taining some of these dried-up Rotifers. On 

 placing a little of the dust in warm water for about 

 half an hour, a number of the Rotifers came out 

 and swam about actively. Rotifers have been 

 known to exist in this dried-up condition for many 



* A second genus of fresh-water Medusae (Limnocnida) has 

 since been found in Lake Tanganyika ED. 



