Chaptp:r 6 

 Variation and heredity 



IT is generally recognized that individuals of a species of 

 organism show a greater or less morphological variation. Pro- 

 tozoa are no exceptions. Various Protozoa manifest a wide 

 variation in a limited or in widely separated localities so that 

 different groups of the same species are spoken of as races, 

 varieties, etc. It is well-known that dinoflagellates show a great 

 morphological variation in different localities. Schroder (1914) 

 showed that there were at least nine varieties of Ceratium 

 hirundinella (Fig. 80) occurring in various waters of Europe, and 

 List found that the organisms living in shallow ponds showed a 

 marked morphological difference from those living in deep ponds. 

 Cyphoderia ampulla is said to vary in size among those inhabiting 

 the same deep lakes, namely, individuals from deep water may 

 reach 200^ in length, while those from the surface water measure 

 only about lOOju long. 



In Foraminifera, the shell varies in thickness even in one and 

 the same species, depending upon the part of the ocean in which 

 they live. Thus the forms which live floating in surface water 

 have a much thinner shell than those which dwell on the bottom 

 of the ocean. For example, according to Rhumbler, Orhulina 

 universa inhabiting surface water has a very thin shell, 1.28- 

 18m thick, while individuals living on the bottom may show a 

 thick shell, up to 24^ in thickness. According to Uyemura, 

 Amoeba sp., occurring in the thermal waters of Japan, showed a 

 distinct dimensional difference in different springs; namely, it 

 varied from 10-40^t in diameter in sulphurous water, and from 

 45-80)u in ferrous water; in both types of water the amoebae 

 were larger at 36-40°C. than at 51°C. Such differences in morpho- 

 logical characteristics appear to be influenced by environmental 

 conditions, and will continue to exist under those conditions, but 

 when the organisms are subjected to a similar environment the 

 differences disappear, as has been demonstrated by many 

 observers. 



Evidences obtained by various investigators point to a general 

 conclusion that when environmental influences are brought upon 



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