OF THE PHTTOZOA. 147 



parent- cell as by a common envelope, and move about as a well-defined body 

 composed of many cells." 



The best accounts of the structm^e of Chlamydomonas we have at hand are 

 those by Perty (op. cit. p. 85), by Eraim (Eejiiv., li. S. p. 214), and by 

 Thuret (Sw les Zoospores, Ann. Sc. Nat. xiv. 1850). Unfortunately, each 

 of these writers describes a different species, which renders our attempt at a 

 general history the more difficult. The figure varies between ovoid and 

 globular ; and the cell is not prolonged at the point from which the pair of 

 vibratile filaments proceed, although a colourless space exists there. The 

 organism consists of a green mass — the primordial cell — surrounded by a dia- 

 phanous delicate envelope, wliich, unlike that of Chlamydococciis, is closely 

 applied to it, so that it leaves no clear interspace between the two. The 

 contents are green globules and larger vesicles, ^ith a single large chlorophyll- 

 utricle in the centre — the nucleus (XIX. 16) — very like in appearance to the 

 starch-globule so frequent in the cells of green Algae. In addition, there is 

 a red stigma, and in some rare instances two such ; in other examples, again, 

 it is altogether wanting. Motion is effected by the ciliaiy filaments, which 

 penetrate the external envelope from the enclosed globule; the envelope 

 resembles that of zoospores in general ; and, like those structures, these uni- 

 cellular beings seek the light and exhale oxygen. 



Perty describes colourless germs from which new specimens originate, — a 

 statement no doubt equivalent to saying that these beings reproduce them- 

 selves by microgonidia, as Cohn represents. Fission into macrogonidia is 

 binaiy or quaternary, as in Tetnispora, and gives rise to two, fom% eight, and 

 even, at times, sixteen or thirty- two individuals. Generally whilst this act 

 proceeds the cells are quiescent, ceasing from their usual movements. This 

 process of multiplication is not influenced by the size of the Chlamydomonads, 

 for it occurs in specimens varying between -j^ to -^-j'". 



Amid the film-like collections of Chlamydomonas, groups of individuals may 

 be encoimtered in various stages of change and of breaking up : some have 

 entirely or partially lost their green contents ; others have acquired a yel- 

 lo'\\'ish-brown, or, more seldom, a red colour ; others are much contracted as 

 small globules within the clear gelatinous cases, whilst others, lastly, acquire 

 a proboscis-like process, or, by pressiu'e, an angular outline. 



The variety and transition of colour just remarked depend upon the phase 

 of existence and the entrance on the resting or quiescent condition. The 

 ceUs of Cldamydomonas ohtusa, Braun teUs us, when swarming are of a dark 

 green coloui', truncate at both ends, and, after multiplying for some time, 

 produce here and there veiy minute paler and more bro^vnish-yeUow micro- 

 gonidia. " In the course of a few weeks no more active cells could be found 

 in the water, the full-gro^Ti swarms having all gradually come to rest and 

 sunk to the bottom. The original longish shape of the cells had changed 

 into a perfect sphere with the transition to rest ; the colour of these resting- 

 cells, origmally green, gradually passed into a light yellowish brown ; at the 

 same time a number of small, sharply- defined, brilliant globules were formed 

 in the interior, ha\TLig quite the appearance of drops of oil. In this altered 

 condition the Chlamydomonads remained, exhibiting neither growth nor 

 increase." It is added, in a note, that these resting (seed) cells are about 

 ■^"' in diameter, have a tough, colourless, and transparent membrane, and 

 finally assume a flesh-red coloiu-. On awakening from this ' resting '-stage, 

 segmentation of the contents re^ives, with the disappearance of the red and 

 oil-like elements. The resting-stage of the microgonidia has not been suffi- 

 ciently investigated, 



Chlamydomonas Pidvisadus. in the opinion of Cohn and most others, is 



l2 



