OF THE PHYTOZOA. 115 



Ehrenberg entertained a similar notion, and called them the testes. ^' Caustic 

 potash," says Cohn (A. N. H. 1852, x. p. 340), "which destroys the rest of the 

 contents of the piimordial cells, makes the chlorophyll-utricles of Stephano- 

 sphctira show themselves more distinctly as hollow rings surroimded by a rather 

 granular membrane ; iodine coloiu's them deep \'iolet, which leads to the con- 

 clusion of the presence of starch." Iodine sometimes, however, produces a deep 

 brown tint (Cohn, R. S. p. 529), due, we may suppose, to an idterior meta- 

 morphosis of the starch, as it is itself a transitional condition of chlorophyll. 



Another stnicture met ^vith among the contents of some of the Phytozoa 

 is the contractile vesicle or sac. This sac has been noticed in Volvox, Gonium, 

 Pandorina, Chilomonas, Cryptomonas, and in Chlamydomonas, and its rhyth- 

 mical contractions observed (XIX. 16, 33 ; XX. 40, 41). In Stephanosphcp.ra 

 a similar vesicle was seen by Cohn, but its contractility not detected : so in 

 Astasia, Euglena (XYIII.), and Polytoma (XX. 1, 2), a clear sac-like space 

 presents itself at the anterior extremity, immediately beneath the surface ; 

 but its alternate expansion and contraction have not been ^vitnessed. 



A nucleus is detected in Euglena, Astasia, Polytoma (XX. 1, 2, 3), and 

 others in which an animal nature predominates. Even among the vegetable 

 genera Volvooc, Pandorina, and Gonium (XIX. 32, 34, 61), most writers, as 

 already seen, seem disposed to view the constant chlorophyll-vesicles as of 

 a nuclear character. In Gonium, indeed, Cohn (Entw. p. 178) describes only 

 one such vesicle, which seems to demonstrate its nuclear natiu^e by breaking 

 up, duiing the process of fission, into as many parts as the primordial cell 

 itself. Braun (op), cit. p. 174, in note) mentions his observation of a central 

 vesicle or nucleus in Chlamydococcus (XIX. 22, 24, 26), and remarks, " in 

 most of the true Pabnellacese there is a chlorophYll-vesicle in the centre of 

 the ceU." 



The appearance of the cells of Phytozoa is much modified by variations in 

 the relative quantity or in the arrangement and colour of the contents, so much 

 so indeed that such varieties have been described as different species or even 

 as different genera. Thus the accidental presence of a red spot, called an eye- 

 speck, or the occurrence of a red central space, have had a specific importance 

 wi^ongly attached to them. The inutility of characters deduced from the 

 disposition and appearance of the cell-contents, or from the figure, is further 

 shown when the effects of external agents — of temperature, of the abundance 

 or deficiency of nutritive matters, of hght, &c. — are taken into account ; and 

 it becomes even stiU more evident when the changes of form one and the 

 same being may undergo are duly considered. 



In a previous page it has been stated that in the earliest phase of existence, 

 when the future cell is but one of several macrogonidia within its mother-cell, 

 the protoplasm of which it consists is unenclosed by a membrane — has no cell- 

 wall. But it would seem that a ceU-membrane is wanting even at maturity 

 in some genera, for example, in Step7ianosp>hcera ; for Cohn writes (A. N. H. 

 1852, x. p. 326), " This is not only made evident by the multifold changes 

 of form which they undergo in the coui^se of vegetation, and by the fihform 

 prolongations and ramifications which are produced directly from theii' sub- 

 stance (XIX. 38, 39-53), but is clearly shown by the transformations which 

 the primordial cells pass through in consequence of external influences. 

 Under certain circumstances namely, the filiform processes may be retracted, 

 being torn away from the envelope -ceU and taken up into the substance of the 

 primordial cells ; the produced ends of the primordial cells also disappear, the 

 latter becoming rounded off into theii' original spherical or short cyhndiical 

 form. Such a change would be impossible if the primordial cells were sur- 

 rounded by a rigid membrane, such as that of the envelope-cell for example." 



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