470 C. F. ROUSSELET ON DISTRIBUTION OF THE ROTIFERA. 



to the above species and some moss-haunting Rotifers of the 

 genera Philodina and Ccdlidina, which habitually live on moss 

 that periodically dries up and then becomes wet again by rain. 

 Species living in always submerged moss do not appear to acquire 

 this property. Another condition of the formation of the pro- 

 tecting gelatinous envelope is that the desiccation should be 

 slow, otherwise it cannot be formed, and the animals die in a 

 short time. 



My experience has shown me, and is confirmed by the experi- 

 ments of D. 1). Whitney, that the vast majority of Rotifers die 

 immediately on being dried, and do not revive after complete 

 desiccation ; but their eggs, and in particular their resting eggs 

 with more resisting shells, can stand a prolonged state of desic- 

 cation and also freezing, and can therefore readily be transported 

 by the wind, or by aquatic birds and other animals, and will 

 hatch when deposited in suitable pools of water. 



In my opinion it is by this means that the cosmopolitan 

 distribution of the Rotifera over the world has in the course of 

 time been mainly brought about. 



The total number of known species of Rotifera may at present 

 be estimated at about 825. In Hudson and Gosse's Monograph 

 of 1886-9, 400 species were described; since that time 527 new 

 species have been named, of which, however, quite a hundred 

 may be deducted as synonyms, or as very doubtful. 



J own. Quekett Microscopical Club, Ser. 2, Vol. X., No. 65, November 1909. 



