SCIENTIFIC SUMMARY. 
121 
apparatus forms a system distinct in itself, and there is no internal gene- 
rative cavity. M. Balbiani, notwithstanding their minute size, succeeded 
in extracting uninjured and subjecting to the action of the surrounding- 
water, some of the young eggs of Paramecium aurelia from the parent 
body, whereupon the egg resolved itself into a vitelline, or yolk, mem- 
brane, and a germinal vesicle. 
Acari in a Nitrate of Silver Bath. — The extraordinary (supposed) dis- 
covery of Mr. Crosse of the generation of acari by electricity has received 
a curious illustration in the experience of Dr. Maddox, who was astonished 
to find, in a twenty-ounce nitrate of silver bath, of forty grains to the 
ounce (for photographic uses), which had been kept for a month in a 
stoppered bottle, a crowd of little acari, sixty or seventy in number, a 
little larger than the cheese-mite. That such conditions should be favour- 
able to the development of germs is certainly extraordinary, and contrary 
to our preconceived notions ; yet we have instances sufficient to show that 
we must not judge of the conditions of the lower classes of animals by 
those which we find obtain in the case of those higher in the scale. 
Migrations of Entozoa. — MM. Pouchet and Vender have been making 
experiments upon the metamorphoses of entozoa, and have come to the 
conclusion of denying the necessary transmission of entozoa as described 
by most modern zoologists, recurring to the old notion that the cystic (or 
bladder-like) worms are produced from germs of Teenise (tapeworms) 
which have found their way into places not fitted for them. If the tape- 
worms of carnivora are due to the cystic worms inhabiting their prey, 
they ask how it is that sheep, which never devour animal food, sometimes 
have their intestines so filled with teniae as to be absolutely obstructed, 
as was the case in 1852, during an epidemic in the sheep about Rouen. 
Again, the number of tapeworms produced often exceeded greatly in 
number the number of worms given. Thus, in one experiment, one hun- 
dred presumed larvae were given to a young dog, taken from its mother, 
and carefully isolated. Twenty days afterwards its intestine contained 
237 teniae, of which the size varied from 4 to GO millimetres. 
Microscopic W riting. — The wonderful machine of Mr. Peters, improved 
by Mr. Webb, has surprised many, even microscopists, by its results. 
The real object of this instrument is to produce micrometric lines, which 
shall serve as tests, being drawn with extraordinary minuteness, and sur- 
prising accuracy ; the squares traced by the intersecting lines contain- 
ing a measurement of no greater than the 16-millionth of an inch, but 
having still sharp and well-defined angles. This is accomplished by a 
comparatively simple instrument, in which lines or curves traced by a 
pencil at the extremity of a long lever, are reproduced on glass by a 
diamond, which, by an arrangement of smaller levers, follows the original 
tracing, but through an infinitely smaller space. Sentences may thus be 
written upon glass, which shall be distinctly legible by the aid of the 
microscope, but yet occupying so small a space that (the number of letters 
in the Bible being known), it is easily computed that the whole Bible and 
Testament could be legibly written, on the same scale, twelve times over 
in the area of a single square inch ! 
