590 DR. R. V. ERLANGER. 
possible to crack the shell with a hammer and to remove it 
with a pair of forceps without injuring the specimen in any 
way. 
The rest of my material was not obtained fresh, but had 
been preserved in spirit. The preservation was satisfactory in 
nearly all cases. 
The stain used was principally alum carmine, which is very 
valuable for molluscs, and can be used to stain in bulk. In 
many cases I used hematoxylin or methyl green as a plasma 
stain. They easily penetrate when only a part of a specimen 
has been prepared for sections. 
Tn most cases I sectionised only the pericardium and the 
mantle cavity, after having removed the foot and other organs 
with a razor or a pair of scissors. In this way a great deal of 
time and trouble may be saved, and the stains penetrate more 
easily. It is of course necessary to have hardened the speci- 
men thoroughly beforehand. By the same method it is easy 
to dissect out the pericardium, mantle cavity, and kidneys. 
Such a preparation can then be mounted whole in balsam, and 
is most useful for the topography of the different organs. 
The sections were cut with Yung’s microtome; the embed- 
ding was done in chloroform and paraffin. Besides dissec- 
tions and sections I also made use of injections, at the special 
request of Professor Ray Lankester. I myself am strongly 
prejudiced against this method, as it is very likely to mislead. 
T used soluble Berlin blue, and injected by blowing the solu- 
tion through a fine glass pipette with the mouth. Applied in 
this way the injections method confirmed the results obtained 
by dissection and sections in every case. When, on the con- 
trary, I used a syringe and a strong pressure, the coloured 
fluid often broke through the walls of the pericardium and 
kidney in places which I consider as loci minoris resis- 
tentia, and which shall be described in the sequel. 
Before beginning my correspondence with Professor Ray 
Lankester on the points at issue I had always injected from 
the pericardium, as morphology and physiology show that the 
liquid which fills the pericardium is expelled by the kidney, 
