STRUCTURE OF THE CELL. 



siasm with which these researches have been pursued by the most competent investi- 

 gators and the great advance in our accurate knowledge concerning the intricate 

 problems relating to the morphology and the physiology of the cell, much pertaining 

 to the details of the structure and the life of the cell still remains uncertain, and must 

 be left to the future achievements in cytology. The account here given of the mor- 

 phology of the cell presents only those fundamental facts which at the present time 

 may be accepted as established upon the evidence adduced by the most trustworthy 

 observers. The more speculative and still unsettled and disputed problems of cy- 

 tology,, interesting as such theoretical considerations may be, lie beyond the purpose 

 of these pages ; for such discussions the student is referred to the special works and 

 monographs devoted to these subjects. An appreciation, however, of the salient 

 facts of cytology as established by the histologists of the present generation is essen- 

 tial not only for an intelligent conception of the structure of the morphological ele- 

 ments, but likewise for the comprehension of the highly suggestive modern theories 

 concerning inheritance, since, as will appear in a later section, the present views 

 regarding these highly interesting problems are based upon definite anatomical 

 details. 



Fig. 5. 



Cytoplasm 



Karyosoiiie 



Linin threads 

 Chromatin 



Spongioplasm 

 Hyaloplasm 



Metaplastic inclusions 



Nuclear membrane 

 Nucleolus 



Centrosome surrounded by 

 centrosphere 



Cytoplasm 

 Cell-wall 



Diagram of cell-structure. 



In the upper part of the figure the granular condition of the cytoplasm is represented; 

 in the lower and left, the reticular condition. 



Notwithstanding the great variations in the details of form and structure, cells 

 possess a common type of organization in which the presence of the cell-body or cyto- 

 plasm and the nucleus is essential in fulfilling the modern conception of a cell. The 

 latter may be defined, therefore, as a iiucleated mass of protoplastn. 



The term protoplasm, as now generally employed by histologists, signifies the 

 organized substance composing the entire cell, and with this application includes 

 both the cytoplasm and the nucleus. 



Structure of the Cytoplasm. — The cytoplasm, or the substance of the cell- 

 body, by no means invariably presents the same appearance, since it may be regarded 

 as established that the constituents of this portion of the cell are subject to changes in 

 their condition and arrangement which produce corresponding morphological varia- 

 tions ; thus, the cytoplasm may be devoid of definite structure and appear homoge- 

 neous ; at other times it may be composed of aggregations of minute spherical masses 

 and then be described as grayiular, or, where the minute spheres are larger and con- 

 sist of fluid substances embedded within the surrounding denser material of the cell, 

 as alveolar ; or, again, and most frequently, the cytoplasm contains a mesh- work of 

 fibrils, more or less conspicuous, which arrangement gives rise to the reticular con- 

 dition. The recognition of the fact established by recent advances in cytology, that 

 the structure of cytoplasm is not to be regarded as immutable, but, on the contrary, 

 as capable of undergoing changes which render it probable that a cell may appear 



