286 W. WOODLAND. 
spicules was as follows :—‘ The specimens were killed in an 
expanded condition by rapid immersion in a ‘5 per cent. 
solution of osmic acid in sea water, were thoroughly washed 
with distilled water and stained for twenty minutes with 
Ranvier’s picro-carmine. The expanded polyps were cut off 
close to their bases, placed in dilute glycerine, and laid open. 
The ectoderm and endoderm having been removed with a 
camel’s-hair brush, very satisfactory flat preparations were 
obtained illustrating the formation of the spicules in the lower 
moities of the exserted portions of the polyps.” My expe- 
rience of this method of making flat preparations of 
Alcyonium digitatum for the study of spicule formation 
is that it is by no means a satisfactory one—certainly not so 
satisfactory as that which I have adopted, and which I will 
shortly describe. For, in the first place, spicules do not 
occur to any great extent in the region of the retractile 
polyps—as, indeed, Bourne admits when he states that “ one 
of the smallest sclerites which I was able to discover is 
shown ... ,” whereas in my own preparations I have been 
able to count such by the dozen—and hence there exists 
a difficulty im observing all the stages of spicule formation ; 
secondly, what spicules do occur here are not very character- 
istic in shape of the greater number of the spicules found in 
the mass of the colony—there existing a tendency for spicules 
situated in the region of the polyps to be smooth and spindle- 
shaped—and hence the development of these others cannot 
from these data be assured. 
Hickson remarks that “ Alcyonium digitatum is not a 
favourable form to take for the study of the development of 
the spicules, as it is a matter of very great difficulty to make 
a thin section of the surface of the colony before decalcifica- 
tion,’ but, owing to the transparency of the mesoglea, it is 
not necessary to cut thin sections for this purpose, as | think 
is proved by the fact that all the figures supplied in the 
plates accompanying the present paper were carefully drawn 
by means of a camera lucida from free-hand sections which 
measured anything from 104 to 504 in thickness. ‘The 
