44 T. C. WHITE ON PUOTOCOCCUS PLUVIALIS. 



placed them finally among the Algae. I cannot give a clearer 

 description of Protococcus than that given by Cohn, in a paper 

 translated for the Ray Society in 1853, entitled "Botanical and 

 Physiological Memoirs." He says, " The moving cell of Frotococcus 

 is composed of two principal parts — a hyaline spherical envelope, 

 formed of a delicate structureless membrane consisting of cellulose, 

 which immediately surrounds the colourless contents, consisting, 

 perhaps, of pure water. In the centre of the envelope occurs a coloured 

 globule composed of the universal nitrogenous protoplasm or 

 mucus of vegetable cells, coloured red or green by a carmine red 

 oil or chlorophyll, and containing in it numerous granules of 

 protoplasm, as well as one or more chlorophyll vesicles. This 

 coloured globule is attenuated at the upper end into a colourless 

 point ; from this point go out two cilia, which protrude into the 

 water through two orifices in the membrance of the envelope, and 

 produce the movements of the whole organism. The inner coloured 

 globule is not bounded by any rigid membrane, but merely by a 

 thickened layer of protoplasm ; hence its contour is very changeable 

 and passes through manifold transformations in the course of its 

 development." This, then, is Cohn's clear and correct description 

 of Protococcus as first presented to the eye of the observer, but 

 changes afterwards take place in them, especially towards winter, 

 when vegetation generally becomes somewhat dormant — changes 

 that may not be passed over because of the interest attaching to 

 their study. Cohn, in the description I have quoted, while mention- 

 ing the fact of Protococci containing red and green colouring 

 matters, does not sufficiently distinguish the areas respectively occu- 

 pied by them. Huxley, in his notice of Protococcus, merely states 

 ** that the individual Protococci may be either green or red, or half 

 green and half red, or the red and green may co-exist in any other 

 proportion." As they were first seen by me, the central coloured 

 globule was a bright green, having a well defined red spot in its 

 centre, but this had the power of diff"using itself at times through 

 the granules of the green protoplasm and colouring it a dull red. 

 After careful watching, this red would be found to have collected 

 again and formed a red area in some other part or parts of the 

 green globule, and not entirely confined itself to the centre. The 

 movement of this Alga under consideration suggests some relation- 

 ship to Volvox, and it indeed belongs to the family of Volvocina. 

 That the green central globule is hollow like Vol vox is evident, as 



