INTRODUCTION 



sidered as apart from the nucleus and when actually existing in an 

 unmanipulated simplest living thing without any nucleus or nuclear 

 matter. We have seen that " plasson " is the name which has been 

 proposed for the latter ; for the former the word " cytoplasm " is 

 frequently used, whilst " nucleoplasm " is applied to that part of the 

 cell-protoplasm which is the nucleus. The use of the word " cyto- 

 plasm " in this sense is certainly objectionable, as it signifies " the 

 cell-plasm " and is merely a synonym of " protoplasm." It would 

 be better to term the extra-nuclear substance of the protoplasmic 

 corpuscle " periplasm." 



As a hypothesis we may assume that living matter was at one 

 time in the condition of " plasson," though it has yet to be shown 

 that " plasson " is in existence at all at the present day. The 

 next hypothetical stage is the development in distinct granular 

 form of the material which later became aggregated as a nucleus. 

 We may apply the word "protoplasm" to this stage, with a 

 qualifying adjective, " konio-karyote " (powder-nucleated). This 

 condition is known as actually existing in certain phases of the 

 ciliate Protozoa (Trachelocerca), and possibly is to be recognised 

 in some degenerate Protophyta and in some of the Proteomyxa 

 (whether degenerate or archaic) amongst Protozoa. The third stage 

 in the hypothetical development of protoplasm consists in the 

 aggregation of the scattered nuclear granules to form one or more 

 nuclei of definite structure and properties. Usually but one such 

 nucleus is formed, but to cover the case of the existence of two or 

 more similarly organised nuclei the term Homokaryote (proposed 

 by Professor Hickson) may be used for this condition. The nucleus 

 of the Homokaryote cell is in leading features of its structure 

 identical with that of the tissue-cells of higher organisms. It 

 consists of nuclear capsule, nuclear hyaloplasm, and of chromatin 

 elements. The optical, chemical, and physiological analysis of the 

 nuclei of Protozoa and Protophyta has not been extended to a 

 sufficient number of instances, at present, to render it possible to 

 trace the steps (if they are still traceable) by which the complete 

 structure of the nucleus and its activity in cell-division were evolved. 

 It is not yet clear whether there are among Protozoa and Proto- 

 phyta any surviving simpler phases of the nucleus, or whether 

 apparently primitive phases which are described are so interpreted 

 owing to incomplete observation or, on the other hand, owe their 

 simplicity to a degeneration from a more highly developed condition 

 of the nucleus. It is, however, certain that there are cases amongst 

 the Protozoa in which the structure and activity of the nucleus in 

 cell-division conforms very closely to those of the tissue-cells of 

 higher animals and plants, if not absolutely identical with them. 



There are, however, in certain Protozoa special modifications of 

 the nuclear structure which have not yet been shown to occur in 



