PROGRESS OF MICROSCOPICAL SCIENCE. 
167 
his opinions on the subject of penetration. To us it appears to be an 
optical defect, but one which is to a certain extent needed in anato- 
mical work, or indeed in any observation where one wishes for more 
than the mere superficial detail. 
However, it will, we hope, be seen that the ' Micrographic Dic- 
tionary ' is by no means the very imperfect work which it was 
represented to be by some critics ; and though we could have wished 
for an improvement in the plates and in some of the articles, still we 
are bound to offer our best thanks to the authors for what we consider 
on the whole a successful re-issue of a very elaborate work on the 
wide field of microscopical research. 
PKOGEESS OF MICKOSCOPICAL SCIENCE. 
How does the Amoeba Simllow its Food? — According to the recent re- 
searches of Professor Leidy (in ' Silliman's American Journal,' Feb., 
1875), some important facts have been arrived at. This observer 
remarked that he had supposed that the Amoeba swallows food by this 
becoming adherent to the body, and then enveloped, much as insects 
become caught and involved in syrup or other viscid substances. He 
had repeatedly observed a large Amoeba, which he supposes to be 
A. princeps, creep into the interstices of a mass of mud and appear on 
the other side without a particle adherent. On one occasion he had 
accidentally noticed an Amoeba with an active flagellate infusorium, a 
Urocentrum, included between two of its fmger-like pseudopods. It 
so happened that the ends of these were in contact with a confervous 
filament, and the glasses above and below, between which the Amoeba 
was examined, effectually prevented the Urocentrum from escaping. 
The condition of imprisonment of the latter was so peculiar that he 
was led to watch it. The ends of the two pseudopods of the Amoeba 
gradually approached, came into contact, and then actually became 
fused, a thing which he had never before observed with the pseudopods 
of an Amoeba, The Urocentrum continued to move actively back and 
forth, endeavouring to escape. At the next moment a delicate film of 
the ectosarc proceeded from the body of the Amoeba, above and below, 
and gradually extended outwardly so as to convert the circle of the 
pseudopods into a complete sac enclosing the Urocentrum. Another 
of these creatures was noticed within the Amoeba, which appeared to 
have been enclosed in the same manner. This observation would 
make it appear that the food of the Amoeba ordinarily does not simply 
adhere to the body, and then sink into its substance, but rather, after 
becoming adherent or covered by the pseudopods or body, is then en- 
closed by the active extension of a film of ectosarc around it. 
The Microscopic Anatomy of Sponges. — Infusoria has been very fully 
given with abundant illustrations in the February number of the 
' American Naturalist,' by one of the editors, Mr. A. S. Packard, jun. 
