38 Mr. J. A. Ryder on the Microscopie 
What, then, is the true state of the case? This query we 
propose answering ; but before we set out it will be necessary 
to give some account of the methods of investigation used in 
order to arrive at a definite conclusion. Thin sections of 
those portions of the animal in which the reproductive struc- 
tures are lodged are of the first importance. After trying 
various methods, which were found for the most part unsatis- 
factory, the preparation of sections was finally conducted as 
follows:—After the soft parts were removed from the shell 
they were thrown into a chromic acid solution of from one to 
two per cent., in which they were allowed to remain for several 
days; and in some cases the hardening solution was even re- 
newed, This was done in order that the hardening agent 
might act upon the whole of the soft parts and harden them 
throughout ; unless the chromic acid is allowed some time to 
act upon the entire animal, it will not be uniformly hardened, 
the centre of the body remaining soft. After hardening, the 
animals should be thoroughly washed and soaked in water for 
a couple of days, to remove all traces of the acid before they 
are finally put into alcohol for permanent preservation. 
Hardened material so preserved will make good sections 
months afterwards. 
Portions of the body-mass of different individuals should 
then be cut out; it is best to cut up the body into thick slices 
or blocks in a transverse direction, large enough to be conve- 
niently held between the fingers. It was also found advisable 
to take such thick slices of the hardened body-mass from 
several individuals, since it was discovered that scarcely any 
two had the reproductive glands developed to exactly the 
same degree of maturity. ‘This point is important, as it bas 
enabled us to follow up the development of the reproductive 
organs in the connective tissue which invests them. After 
considerable experiment and disappointment in the effort to 
imbed these thick hardened slices so as to cut sections with 
the microtome, the method of imbedding was abandoned alto- 
gether. ‘he thick blocks or slices were entirely freed from 
alcohol by soaking in water for a day, then removed, after 
drying them off as much as possible with blotting-paper or a 
soft linen cloth, to a thick solution of gum arabic, in which it 
is best to allow them to remain from twenty-four to forty-eight 
hours, so as to be thoroughly saturated. The superfluous 
gum may then be poured off and the blocks of tissue, soaked 
as they are with the gum, covered with strong alcohol. In 
twenty-four hours the blocks will be found hard enough to 
cut. ‘The blocks of hardened tissue are simply held between 
the thumb and fore finger, and thesections made with a section- 
