10 C. F. ROTJSSELET ON PRESERVING ROTATORIA. 



at a great rate. This must be followed after one or two 

 minutes by continuous further doses until the cilia cease to 

 move and the colonies become motionless, which is accom- 

 plished in five to ten minutes. They are then killed quickly 

 with osmic acid, which must be allowed to act for half-a- 

 minute, washing out in water rather quickly, otherwise the 

 animals separate, although perfectly preserved. The gela- 

 tinous substance in which these Rotifers are embedded also 

 swells somewhat in formalin, and it is, therefore, advisable to 

 preserve the colonies in the sublimate and salt solution, and 

 mount them in that fluid. 



Asplanchna priodonta can be narcotized very quickly. Five 

 minutes after the first dose the animals receive continually 

 fresh doses until they swim very slowly, and are killed whilst 

 still moving, all fully extended, almost without exception, the 

 whole process being finished in about ten minutes. 



Asplanchnopus myrmeleo must remain about half-an-hour 

 under the influence of the narcotic, until the cilia beat very 

 feebly, and the animals are hardly able to move. 



Not ops brachionus requires a good dose of coca'in- alcohol 

 mixture to begin with, and after ten minutes more and more 

 doses until they gradually fall to the bottom and are unable to 

 swim ; but as long as the cilia beat with force they will con- 

 tract, and they must, therefore, be closely watched and killed 

 at the moment when the cilia have stopped moving in some of 

 the animals. 



Euchlanis. With coca'in alone I had no success at all with 

 the various species of Euchlanis, but with the cocam-alcohol 

 mixture I have been able to prepare all the species without 

 difficulty. They must be narcotized very quickly by adding 

 large doses, and killed whilst still swimming about, otherwise 

 they gradually contract. 



Brachionus pala is readily killed fully extended, either by 

 narcotizing quickly or slowly. 



Brachionus urceolaris, on the other hand, is quite spoiled by 

 the slow process, and must be narcotized as quickly as possible 

 with large doses of the narcotic until the animals become 

 motionless, when they are quickly killed and fixed with a drop 

 of osmic acid. 



Synchwta tremula and similar illoricate free swimmers can be 

 narcotized fairly quickly in 10 to 15 minutes, and killed whilst 



