Nuclear Divisions in Amoeba pro tens. 



By 

 Monica Taylor, S.N.D. 



With Plate 2. 



No definite answer, so far as I have been able to ascertain, 

 has yet been given to the question that is inevitably provoked 

 by the spectacular rapidity with which amoebae increase in 

 number in laboratory cultures, viz. ' How does the nucleus 

 divide ? ' In attempting to answer this question it is important 

 to remember, a fact which five years' experience in cultivating 

 amoebae on a large scale has taught, that the most luxuriant 

 cultures are subject to periods of depression. Unless the 

 necessary precautions be taken (5) they die down and remain 

 dormant for a varying period of time, then gradually recover. 



The amoebae which first appear in such ' recovering ' cultures 

 are minute. When they have attained full size they multiply 

 at a great rate, luxuriance being eventually again established 

 in the culture. Divisions of the nucleus by fission must there- 

 fore be distinguished from nuclear divisions connected with the 

 ' sporulation ' process. 



It will be useful to recall at the outset the ' resting ' nucleus 

 and its behaviour in a living amoeba. In the following account 

 the descriptions given by Doflein (3), ychaeffer (4), Carter 

 (1, 2), having been verified, are embodied for the sake of viewing 

 the subject as a whole. 



The nucleus is a large discoid body which is rolled over 

 passively by the streaming endoplasm. Its membrane is 

 strongly marked. Immersed in the nuclear sap is (i) a centrally 

 placed, plate-like, conspicuous karyosome which lies in a highly 

 vacuolated achromatic substance, and (ii) the chromatin. 

 The chromatin, according to Doflein (3) and Hchaeffer (4), is 



