224 



PROTOZOOLOGY 



(1934) distinguished 12 such varieties and showed that any variety 

 could be changed into another by using different culture media. This 

 transformation, however, did not occur at the same rate among dif- 

 ferent races. It was found that the longer a strain has remained under 



Fig. 94. Varieties of Ceratium hirundinella from various European 

 waters (Schroder), a, furcoides-type (130-300> by 30-45/x); b, brachy- 

 ceroides-type (130-145/z by 30-45^); c, silesiacum-type (148-280/x by 

 28— 34ju) ; d, carinthiacum-type (120-145/z by 45-60/x); e, gracile-type 

 (140-200/* by 60-75/x); f, austriacum-type (120-160/x by 45-60/x); g, 

 robustum-type (270-310/x by 45-55/x); h, scotticum-type (160-210/z by 

 50-60m); i, piburgense-type (180-260/* by 50-60/x). 



conditions producing a given type, the greater the time and the num- 

 ber of generations needed to change it to a new type under a new 

 condition, as is shown in Table 9. 



While in many species, the races or varieties have apparently been 

 brought about into being under the influence of environmental con- 

 ditions, in others the inherited characters persist for a long period, 

 and still in others the biotype may show different inherited char- 



