PHARYNGEAL GLAND OF THE EARTHWORM 39 
all the mucin appears red ; in two to seven minutes the mucin is 
stained red, while all the rest of the tissue is stained blue. It is 
better to examine the sections while they are still in the solution 
of Thionin, as it is very difficult to mount them without des- 
troying the metachromasy. There are, however, several ways 
of mounting the slides in Canada balsam, by which the meta- 
chromatic effect may be retained for at least seven days. I shall 
mention only the following few methods which have given me 
very satisfactory results. 
(1) Very rapid passage through absolute alcohol, xylol, and 
mounting in Canada balsam. 
(2) Sections stained in Thionin, washed rapidly in distilled 
water, fixed in a 10 per cent. aqueous solution of Potassium 
ferrocyanide (Krause’s method), rewashed in distilled water, 
and then passed rapidly through the graded alcohols, absolute 
alcohol, and xylol, into Canada balsam. 
(3) The sections are staimed by the previously deseribed 
Thionm method, before freemg them from paraffin, washed 
rapidly in distilled water, dried thoroughly with filter paper, 
and then freed from paraffin and mounted in Canada balsam. 
(4) Instead of alcohol, Acetone is used for dehydration, and 
xylol for clearing ; and the sections are then mounted in Canada 
balsam (method recommended to me by Dr. W. H. Harvey). 
Mounting the sections in levulose syrup, or syrup of Apathy, 
is not advisable, for even when it preserves the metachromasy, 
sections thus prepared do not show clearly the cytological 
structure, particularly under examination with high magnifica- 
tions. I did not succeed in differentiating the sections with 
Hari’s mixture (1901). Finally, the use of artificial light for 
examination of the sections is strongly recommended, as it 
shows a more striking contrast between the red and the 
blue colours of the staimed sections. 
3. THE STRUCTURE OF THE PHARYNGEAL OR SALIVARY BULB. 
The pharyngeal bulb has been already morphologically de- 
scribed by several authors who have dealt with the anatomy of 
earthworms. In almost all species of earthworms, it has the 
