K'. 
doctrine of evolution, I do not hesitate to give a short resume of 
their labours. 
lliey remark that in studies of this kind, it is necessary that 
they should be made without a break in observation, through all 
the changes that the form under examination may undergo, and 
then by repeating the observations, decide on the stability or other* 
wise of the form, bor work of this kind to be effective there must bo 
more than one observer, in order that these observations may be un- 
broken as far as possible, and also to secure a mutual as well as a 
double confirmation. In order to carry out these observations, 
they employed an arrangement by which they were enabled to 
keep the same drop of fluid under examination from eight to four- 
teen days, when placed under the highest powers of the microscope. 
The form examined was obtained by macerating a cod’s head for .some 
months. The striking similarity of form and structure in all the ex- 
tremely minute monads, makes distinction of form almost impossible, 
whilst the tendency of individuals to vary from the type form, 
makes it unsafe. But physiologically and morphologically the 
recurrent cycle of sequence is unerring. 
Ihe foim of this monad is described by the author a.s bein^^ a 
*■ O 
long oval inclined to an egg shape ; at the narrow end a sharp 
conical projection might be observed, and from it proceeds a 
delicate flagellum, about twice the length of the body ; under this a 
longer flagellum may be detected, by means of which it is enabled 
to anchor itself. Its mode of increase, and at one time supposed 
to be its only one, is by fission, but by long and continuous obser- 
vation, they detected the conjugation of the free form. The 
authors remark that “ the form on which our constant labour had 
been bestowed, passed through a series of remarkable changes, all 
and every one of which might be taken for a distinct and inde- 
pendent creature, but that we have traced it through all its transi- 
tions, and seen it pass from one into the other. We find that 
. these changes are always alike. The stability of their recmrence is 
as complete as that of any entomological form. But Ave had one 
very important investigation to complete. On this we were work- 
ing with the highest powers, when our attention was arrested by 
