350 Illinois State Laboratory of Natural IHstori/. 



with a "cocaine-spirit mixture," made according to the fol- 

 lowing formula : 



2% solution of cocaine 30 parts. 



Methylated spirit 10 parts. 



Water 60 parts. 



Just before the cilia stop vibrating the rotifers are killed 

 with a ^ %y solution of osmic acid, in which they are kept for 

 about half a minute, after which they are thoroughly washed 

 in water'from a few minutes to half an hour and are then 

 permanently preserved in a 2^'\, solution of formalin. 

 This is an aqueous solution of formaldehyde and as prepared 

 for sale has a strength of 40 ^\,. The species which have 

 gelatinous tubes are more satisfactorily preserved in a mix- 

 ture of equal parts of a -j^o/o solution of corrosive sublimate 

 and a ^ % solution of common salt, since formalin extends 

 the tubes to two or three times their natural length. In 

 place of cement cells for permanent mounting, Mr. Rous- 

 selet uses slides with concave centers and fastens the cover- 

 glass by means of Miller's caoutchouc cement.* 



OEOdlUPHICAL DISTRIBUTION. 



The Rotlfera are cosmopolitan in their range, being found 

 in all parts of the world. They inhabit mostly fresh water, 

 but a number of species are found in the sea. Some of the 

 species, such as Rotifer rid:/(iris and Hijdatina senta, appa- 

 rently occur in all parts of the world. There seems to be 

 something about the organization of the rotifer that enables 

 it to thrive under a great variety of conditions. The same 

 forms are found in both rivers and muddy ponds in the 

 United States, in clear streams of Europe or even in Alpine 

 lakes, in the rivers of Egypt, and in the reservoirs of India. 

 Climate and temperature seem to have little effect upon 

 the distribution of rotifers. 



FOOD llELATIONS. 



The rotifers play an important part in the economy of 

 nature, since they evidently take a prominent position among 



*1 find that Brown's trunsparent rubber cement answers this purjiose very well. 



