No. 589] 



THE EVOLUTION OF THE CELL 



37 



regard to the functions of the nuclear and cytoplasmic con- 

 stituents of the cell are now well known and are cited in 

 all the text books. It is not necessary, therefore, that I 

 should discuss them in detail. I content myself with 

 quoting a competent and impartial summary of the results 

 obtained : 



A fragment of a cell deprived of its nucleus may live for a consid- 

 erable time and manifest the power of coordinated movements without 

 perceptible impairment. Such a mass of protoplasm is, however, devoid 

 of the powers of assimilation, growth, and repair, and sooner or later 

 dies. In other words, those functions that involve destructive metabolism 

 may continue for a time in the absence of the nucleus ; those that involve 

 constructive metabolism cease with its removal. There is, therefore, 

 strong reason to believe that the nucleus plays an essential part in the 

 constructive metabolism of the cell, and through this is especially con- 

 cerned with the formative processes involved in growth and develop- 

 ment. For these and many other reasons ... the nucleus is generally 

 regarded as a controlling centre of cell-activity, and hence a primary 

 factor in growth, development, and the transmission of specific qualities 

 from cell to cell, and so from one generation to another. 20 



I may add here that the results of the study of life-cycles 

 of Protozoa are entirely in harmony with this conception 

 of the relative importance of nuclear— that is chromatinic 

 —and cytoplasmic cell-constituents, since it is not infre- 

 quent that in certain phases of the life-cycle, especially in 

 the microgamete-stages, the cytoplasm is reduced, appar- 

 ently, to the vanishing point, and the body consists solely 

 of chromatin, so far as can be made out. In not one 

 single instance, however, has it been found as yet that any 

 normal stage in the developmental cycle of organisms con- 

 sists solely of cytoplasm without any particles of chro- 

 matin. 



While on the subject of physiological experiment, there 

 is one point to which I may refer. Experiments so far 

 have been carried on with Protozoa possessing definite 

 nuclei. It is very desirable that similar experiments 

 should be conducted with forms possessing chromidia in 

 addition to nuclei, in order to test the physiological capa- 



20 E. B. Wilson, "The Cell," second edition, 1911, pp. 30 and 31. 



