ii PRACTICAL DIRECTIONS 259 



life-history : and then a balance must be struck and the 

 doubtful form placed in the kingdom with which it has, on 

 the whole, most points in common. 



It will no doubt occur to the reader that, on the theory 

 of evolution (p. 222), we may account for the fact of the 

 animal and vegetable kingdoms being related to one another 

 like two trees united at the root, by the hypothesis that the 

 earliest organisms were protists, and that from them animals 

 and plants were evolved along divergent lines of descent. 



PRACTICAL DIRECTIONS. 



Sph.8Brella. Examine a drop of water containing Sphserelhe (see 

 note on p. 238), first with the low power, and then, after putting on 

 a cover-glass, with high power. Note 



1. Their founded form and green (or red) colour ; the thick cellulose 

 cell-wall ; the protoplasm, enclosing (a) chroviatophores containing 

 chlorophyll (the red colour is due to another colouring matter, hczmato- 

 chrome}, and (b] a central nucleus, seen better later ; and in the active 

 forms, the \.wflagella. Sketch. 



2. Dissolve out the chlorophyll by adding alcohol ; the nucleus will 

 then be visible, and may be made more distinct by staining with 

 magenta, or a solution of potassic iodide in water, saturated with 

 iodine. After treatment with the iodine solution, a bluish coloration 

 will often be seen around the small starch-containing pyrenoids. 



3. Treat some specimens either with strong iodine solution and then 

 with sulphuric acid (75 per cent.), or with Schulze's solution, which is 

 prepared as follows : make about 25 c.c. of a syrupy solution of zinc 

 chloride, and let it stand for a short time ; then pour off the clear fluid, 

 saturate it with potassium iodide and add iodine until the solution has 

 about the colour of sherry. Note the blue coloration of the cell-wall. 



4. In the living specimens note also the mode of division into 

 4 megazooids or into numerous microzooids, and observe their move- 

 ments when set free. Sketch. 



Euglena. Examine a drop of water containing Euglena with the 

 low power, then cover, and put on the high power. Note 



I. The spindle-shaped form of the body, and its changes of form in 

 contraction and expansion. 



S 2 



