196 Modern Microscopy 



organized sparks of life instead of letting them die and 

 disappear in a few days. For a close study of this group, 

 ■well-preserved type specimens are of the greatest possible 

 assistance and importance, and if such had existed formerly 

 much confusion and inexactitude in their description and 

 classification would have been avoided, particularly in the 

 giving of three or four different names to the same species, 

 which causes so much trouble to the student. 



The total absence of type specimens of rotifers to refer 

 to when required, originally led to an attempt on the part 

 of Mr. C. F. Eousselet to produce them, and it is now over 

 ten years since the first successful experiments at pre- 

 serving them in a fully extended and natural state were 

 made. His method, although so simple now, took fully 

 three years to work out until the right and most suitable 

 narcotic, fixing agent, and preserving fluid were found. 

 By the use of suitable fixing agents not only the external 

 shape of rotifers can be preserved, but also all the internal 

 structure to the minutest anatomical details, such as the 

 striated muscle fibres, nerve threads, vibratile tags or flame 

 cells, sense hairs, cilia, etc., and frequently important 

 details can be more readily observed than in the living 

 animal. 



Narcotizing. — As is well known, no killing agent is 

 sufficiently rapid to prevent the complete retraction of 

 rotifers, and few other animals can contract into such a 

 shapeless mass when we attempt to kill them by ordinary 

 means, such as poisons, alcohol, heat, etc. It is, therefore, 

 necessary to use first a suitable narcotic, which has been 

 discovered in hydro-chlorate of cocaine. As a result of 

 many trials, the best solution for most rotifers has been 

 found to be the following mixture : 



2 per cent, solution of hydrochlorate of cocaine, 3 

 parts ; 



Alcohol (or methylated spirit), 1 part ; 



Water, 6 parts. 



Another narcotic which is also very suitable for rotifers 



