246 F. 0. EOWEE. 



found in Closterium. In the various complicated forms which 

 are thus produced there may still he recognised a rod like 

 central portion, which, however, is sometimes so short as to be 

 almost splierical. The stellate form which is thus attained has 

 long been known as characteristic of Zygnema (fig. 16). 



Though the chromatophores are so variable in form, their 

 arrangement and distribution within the individual cell are 

 usually constant, and only in few Algae has it been found that 

 they move from place to place (e.g. in many Siphonese). An 

 analogous regularity of arrangement holds also for the cell 

 nuclei ; and the conclusion forces itself upon the observer that 

 there is often a certain mutual dependence between the two 

 organs in the cell, inasmuch as the position of the nucleus is 

 clearly determined by the arrangement of the chromatophores. 

 It appears that the chromatophores are always completely 

 enclosed by colourless protoplasm, though it is often difficult 

 to be certain of this point. 



The minute structure of the chromatophores shows great 

 uniformity : when in the living state, whether they be green or 

 red or brown, they usually appear under high powers as quite 

 homogeneous, and without any special internal structure. Still 

 their substance is never quite transparent, and sometimes has 

 a finely dotted appearance, as though there were a very finely 

 porous, or reticulated structure. This appearance is heightened 

 after killing by reagents. Professor Schmitz finds the chroma- 

 tophores to consist of a ground substance allied to protoplasm, 

 and colouring matters diffused through it; and he gives as his 

 opinion that the colouring matter does not fill the cavities of 

 the network, but that the reticulated ground-substance is itself 

 permeated by the colouring matter. 



Many chromatophores are without further peculiarities of 

 internal structure : e.g. most Floridese, many Phseophycese, 

 all Characese, and some Chlorophyceae, Vaucheria, Codium, 

 Botrydium. In other cases including the large majority of green 

 Algae, one or several, usually spherical bodies are embedded in the 

 chromatophore, just as nucleoli in the body of the nucleus (fig. 

 15). These are termed Pyrenoids (7rvpr)v — stone of a fruit) . In 



