Opalina. 217 
elongated, or irregular in form and are of various sizes; that they 
lie usually |in this species] in a regular direction in the whole body, 
the flat side of the disc [when they are disc-shaped| being parallel 
to the surface of the body, so that in sections parallel to the flattened 
surfaces of the body one sees them almost all circular, while in other 
sections they appear almost all rod-shaped; that they appear homo- 
geneous when strongly stained with [most] aniline dyes; but not so 
with [well extracted] iron-haematoxylin; that they show an alveolar (?) 
structure; that one often finds them constricted in the middle like 
a dumb bell; that they are insoluble in alcohol, alcohol and ether, 
strong acetic acid, or weak mineral acids; that they are soluble in 
concentrated mineral acids. I can add that they are but slightly 
colored by osmic acid; that they are insoluble in cold water; that 
they are insoluble in tannic acid; that after boiling with hydrochloric 
acid or after digesting them with diastase, the solution gives no 
sugar reaction with Frxsure’s solution (not a very delicate test); 
that they do not stain at all with potassium iodide; and that for 
the most part they do not stain with iodine dissolved in a water 
solution of potassium iodide, though occasionally some of them in 
some part of the body stain a good brown with the iodine solution.’) 
It is of interest that, when treated with this iodine solution, 
most of the individuals of O. ranarwm used for experiment did not 
stain at all; a few showed brown color in some large irregular 
masses which seemed to be on one side or the other of the boundary 
between ectosare and endosarc, probably in the endosarc; many 
showed a diffuse brown stain in the endosare in one or more regions 
of the body, this diffuse stain usually not affecting the spherules, 
though in a few instances the spherules in these stained areas were 
themselves tinged with brown. Heat does not change the stain; 
adding strong sulphuric acid darkens it but slightly and does not 
give a red or violet tone. 
In O. caudata there is no color reaction to potassium iodide; 
the reaction to iodine dissolved in a water solution of potassium 
iodide is similar to that described in O. ranarwm, except that I found 
that the whole endosarc in all individuals stained strongly and a 
more reddish brown, the ectosare, like that of O. ranarum showing 
only a faint yellow tinge. Addition of strong sulphuric acid darkens 
*) Glycogen is said to stain reddish brown with potassium iodide or with 
iodine, the color disappearing upon heating. If sulphuric acid be added to the 
stained glycogen the color is said to become redder or show a violet tone. (See 
especially Barrurta 1885.) 
