54 



THE CELL 



threads, a few of which are extended throughout the nuclear 

 space. A considerable time before division occurs, the nuclein 



A 



B 



C 



D 



Fig. 32. A Resting nucleus of a primitive sperm cell of Ascnris megalocephala bivalens ; 

 B nucleus of a sperm mother cell from the commencement of the growth zone ; C resting 

 nucleus of a soerm mother cell from the growth zone; D vesicular nucleus of a sperm 

 mother cell from the commencement of the dividing zone just before division. 



becomes arranged in definite threads (D). A nucleolus is always 

 present in the meshes of the framework. 



III. Are there Elementary Organisms existing without 

 Nuclei ? The important question, as to whether the nucleus 

 is an indispensable portion of every cell, follows naturally on 

 the description of the chemical and morphological properties of 

 the nucleus. Are there elementary organisms without nuclei ? 

 Formerly investigators were not at a loss to answer this question. 

 For since, in consequence of the inadequacy of former methods of 

 examination, no nuclei had been discovered in many of the lower 

 organisms, the existence of two different kinds of elementary cells 

 was assumed : more simple ones, consisting only of a mass of 

 protoplasm, and more complex ones, which had developed in 

 their interior a special organ, the nucleus. The former were 

 called cytodes by Haeckel (I. 10; II. 15), to the simplest, solitary 

 forms of which he gave the name of Monera; the latter he called 

 cellula?, or cytes. But since then the aspect of the question has 

 become considerably changed. Thanks to the improvements in 

 optical instruments, and in staining methods, the existence of 

 organisms without nuclei is now much questioned. 



In many of the lower plants, such as Alga? and Fungi, and 

 in Protozoa, Yampyrella, Polythalamia, and Myxomycetes, all 

 quoted formerly as examples of non-nucleated cells, nuclei may 

 now be demonstrated without much trouble. Further, since 

 the nucleus has been discovered in the mature ovum (Her twig 

 II. 19 a), we may safely say that, in the whole animal kingdom, 

 there is not a single instance where the existence of a cell with- 

 out a nucleus has been proved. I shall probably be confronted 

 with the red corpuscles of Mammals. It is true that they contain 

 no nuclei, but then neither do they contain any true proto- 



