OCTOPUS ARM, REGENERATION AND STRUCTURE 3 
attention must be paid to this, as otherwise air penetrates the 
tissues. The presence of air in the tissues renders their impreg- 
nation with paraffin or other media extremely difficult, and thus 
the microtome work very unsatisfactory. Combinations of 
celloidin and paraffin and also of collodium and paraffin proved 
the most practical substances for embedding. The pieces after 
being well drained in alcohol (100 per cent) were placed in a 
mixture of equal parts of aleohol and ether, and remained there 
for several hours. They were then put into a diluted solution 
of celloidin or collodium for 24 hours. The pieces impregnated 
with collodium were then left in oil of origanum for 24 hours, 
and the celloidin pieces were submitted to the same treatment 
in cedar oil. Later they were immersed in a mixture of oil of 
origanum plus 40° paraffin, and cedar oil plus 40° paraffin, 
respectively, and remained in these mixtures for twenty-four 
hours. Thereupon they were placed in several baths of paraffin 
of different degrees, and finally in 58° paraffin, in which they were 
embedded. The 100 per cent alcohol had hardened the tissues 
to such a degree that microtoming was exceedingly difficult. 
It was therefore necessary to employ mastic-collodium. No albu- 
minous glycerin, only distillated water was used for mounting. 
The slides were further treated in the usual way. Photoxolin 
was not used; on the contrary, the mastic-collodium was removed 
by a solution of equal parts of aleohol and ether. The sections 
were stained on the slide with haemalaun (Mayer) haematoxylin 
(Heidenhain), eosin, orange G several of the specimens fixed 
in osmic, were stained saffranin plus emerald green. The best 
stains were obtained by a combination of haematoxylin (Heiden- 
hain) plus eosin. Some specimens were stained by way of 
impregnation, according to the method of Bielschowsky and 
Maresch. 
THE FINER STRUCTURE OF THE ARM 
The anatomy of the arm of the cephalopods has often been 
made the object of closer study. Cuvier’s publication 1817 
gives quite a minute description of it. Since then a number of 
authors have devoted their attention to the same subject. Colo- 
