212 PROTOZOOLOGY 



Regeneration 



The capacity of regenerating the lost parts, though variable 

 among different species, is characteristic of all Protozoa from simple 

 forms to those with highly complex organizations, as shown by ob- 

 servations of numerous investigators. It is now a well established 

 fact that when a protozoan is cut into two parts and the parts are 

 kept under proper environmental conditions, the enucleated portion 

 is able to carry on catabolic activities, but unable to undertake ana- 

 bolic activities, and consequently degenerates sooner or later. Brandt 

 (1877) studied regeneration in Actinosphaerium eichhorni and found 

 that only nucleate portions containing at least one nucleus regener- 

 ated and enucleate portions or isolated nuclei degenerated. Similarly 

 Gruber (1886) found in Amoeba proteus the nucleate portion regener- 

 ated completely, while enucleate part became rounded and perished 

 in a few days. The parts which do not contain nuclear material may 

 continue to show certain metabolic activities such as locomotion, 

 contraction of contractile vacuoles, etc., for some time; for example, 

 Grosse-Allermann (1909) saw enucleate portions of Amoeba verrucosa 

 alive for 20 to 25 days, while Stole (1910) found enucleate Amoeba 

 proteus living for 30 days. Clark (1942, 1943) showed that Amoeba 

 proteus lives for about seven days after it has been deprived of its 

 nucleus. Enucleated individuals show a 70 per cent depression of 

 respiration and are unable to digest food due to the failure of zymo- 

 gens to be activated in the dedifferentiating cytoplasm. According to 

 Brachet (1950), the enucleated half of an amoeba shows a steady 

 decrease in ribonucleic acid content, while the nucleated half retains 

 a much larger amount of this substance. Thus it appears that the 

 synthesis of the cytoplasmic particles containing ribonucleic acid is 

 under the control of the nucleus. 



In Arcella (Martini; Hegner) and Difflugia (Verworn; Penarcl), 

 when the tests are partially destroyed, the broken tests remain un- 

 changed. Verworn considered that in these testaceans test-forming 

 activity of the nucleus is limited to the time of asexual reproduction 

 of the organisms. On the other hand several observers report in 

 Foraminifera the broken shell is completely regenerated at all times. 

 Verworn pointed out that this indicates that here the nucleus con- 

 trols the formation of shell at all times. In a radiolarian, Thalassi- 

 colla nucleata, the central capsule, if dissected out from the rest of 

 body, will regenerate into a complete organism (Schneider). A few 

 regeneration studies on Sporozoa have not given any results to be 

 considered here, because of the difficulties in finding suitable media 

 for cultivation in vitro. 



