The incipient nucleus 5 



proof that it had the same function as the nucleus of higher plants. Deiniga ('91) did 

 not assign to the central body the function of a nucleus, because, like Zacharias, he could 

 not demonstrate its presence in all the cells of a filament. Palla ('93) found no chromatin 

 in the central body, and regarded it as questionable whether it should be regarded as 

 a nucleus or not ; but he also added that the direct division may be more complicated 

 than it appears to be. Massart ('02) affirmed that there was no reason to consider it as 

 a nucleus owing to its vacuolation and indefinite outline. Macallum's investigations ('99), 

 were mainly negative, and he believed that there was no cell-nucleus or any structure 

 resembling one. Fischer ('05), in a very suggestive paper, also denies the existence 

 of a nucleus. He describes, however, what he terms a ' carbohydrate mitosis ' (or 

 ' pseudomitosis of anabsenin ') which is an equal division of carbohydrate reserves by 

 means of simple mitotic dispositions, but this interpretation of any of the structures 

 described as occurring in the myxophycean cell has never been supported, whereas there 

 is much evidence to the contrary. 



II. In contrast to the opinions just enumerated, Wille ('83), Zacharias (in one of 

 his earlier papers in 1885, the views in which he afterwards repudiated) and Scott 

 demonstrated to their own satisfaction the presence of a body of a nuclear character. 

 Hegler ('01) considered that his investigations conclusively proved that the central body 

 was a nucleus. It consisted of a faintly stainable ground substance in which small 

 granules were loosely embedded. The granules he regarded as chromatin because their 

 behaviour during division, and towards stains and reagents, agreed in all respects with 

 the behaviour of the chromatin of the nuclei of more highly organized cells. The nucleus, 

 he stated, differs from that of higher types in the absence of a nuclear membrane and 

 a nucleolus. Kohl ('03), as the result of some very careful work, states that the Blue- 

 green Alga3 possess a nucleus which differs from that of higher plants not only in the 

 absence of a nuclear membrane and nucleolus, but also in its remarkable form. It 

 possesses numerous radiating outgrowths of a pseudopodium-like character, which some- 

 times extend as far as the cell-wall and are retracted if the fixation is slow. It also 

 contains a number of granules of albuminous material, the ' central granules,' and 

 chromatin is always present distinct from other inclusions. Phillips ('04) regarded the 

 central body as a true nucleus with chromatin in the form of hollow vesicles in the resting 

 cell. Olive ('05) also stated that the central body was a true cell-nucleus. 



The three last-named authors have each described a mitotic division of the declared 

 nucleus during which a rudimentary spindle and rudimentary chromosomes can be 

 demonstrated. 



Gardner ('06) also considered the central body as a nucleus consisting of granules and 

 chromatin embedded in an achromatic ground substance. He described three types of 

 nuclear structure: (1) some forms (e.g. the large, short-celled species of Oscillatoria) in 

 which the chromatin is disposed in the ground substance in the form of disconnected 

 masses ; (2) others (e.g. Symploca muscorum) in which it is partially united into a coarse, 

 thread-like mass ; and (3) still other cases (e.g. Dennocarpa) in which the chromatin 

 is united into a definite network (fig. 4). The division of the nucleus was in all cases 

 amitotic, with the possible exception of Synechocystis (fig. 8). 



III. Between the extreme views of the above-mentioned authors there are the 

 carefully considered opinions of those who regard the central body as a nucleus of a 

 primitive or rudimentary kind. Hieronyrnus ( ; 92) demonstrated the presence of granules 

 in the central body, which, although not identical with chromatin, performed the functions 

 of chromatin, and he also described the presence of vacuoles. He was the first to point 

 out the absence of a nuclear membrane, and he suggested that the central body might 



