258 
NOTES AND MEMORANDA. 
slight motion, for the most part in slight curves. Whenever the 
contractile reservoir became contracted, which occurred pretty regu- 
larly at intervals of about half a minute, and took place very sud- 
denly, there succeeded a jerking kind of acceleration of the forward 
movement. If the animal happened to be previously stationary, it 
made a jerking forward movement at the instant of the systole of about 
a quarter its length. A simultaneous acceleration of the very slug- 
gish ciliar motion could not be discerned at all. The phenomenon 
can only be explained, therefore, by the rebound caused by the fluid 
ejected from the contractile bladder at the systole. 
With this harmonizes the fact that the hindermost section of the 
body shrunk together at the systole into a thin, empty, longitudinally 
folded sac, without there being any appearance of even the slightest 
increase of volume of the front part of the body. It is certain, there- 
fore, in the case before us, that a very large portion, perhaps the whole 
quantity, of the fluid contents of the contractile bladder was emptied 
outwards during the systole. 
As the re-expansion of the bladder, as is generally the case, took 
place very slowly, it could not be decided whether any fluid could be 
directly sucked in from without. He considers this, however, to be 
highly improbable, amongst other reasons, because he never succeeded 
even with other species in seeing the contractile vacuoles fill them- 
selves with coloured fluid from that which surrounded them.* 
White of Egg as an Imbedding Substance . — The best substance for 
imbedding small objects with a view to the preparation of sections is 
one that can be hardened to any required degree, is easily cut, is 
transparent, and allows of the section being placed in balsam or 
dammar immediately after it is prepared. 
These requisites are found in the ordinary white of egg of the 
fowl. 
The object to be imbedded (which is best stained beforehand) 
must have lain for one or more hours, according to its size and pene- 
trability, in white of egg, so as to become thoroughly penetrated by it. 
There must be no alcohol left in the object, as it gives rise to blisters 
in the course of the subsequent process, and thereby produces holes 
in the imbedding substance. 
The object thus soaked is now placed in an oblong box of stiff 
close-made paper folded or pasted together filled with the albumen. 
The position of the object may be fixed if necessary by a needle 
passing through the upper part of the box, which can be easily with- 
drawn after the hardening. 
The box thus filled must be exposed to hot steam or, still better, to 
hot air. After about twenty minutes the albumen becomes hard 
enough, and the box should then be put into strong sjnrit, which in 
the course of a few days must be changed once or twice, to be finally 
replaced by absolute alcohol. Several days after this treatment the 
objects are ready for cutting. The paper walls of the box may be 
removed with a knife, and a section of the hardened albumen several 
* ‘ Zoologischer Anzeiger,’ vol. i. p. 121. 
