528 
POPULAll SCIENCE REVIEW. 
Antiquity of Desmidcce and Diatomacece . — An examination of thehornstone 
nodules of the Devonian and Silurian rocks of New York has resulted in the 
discovery of abundant organisms referable to the Desmideae, such as numerous 
forms of Xanthideae, supposed to he the sporangia(l) of Desmids, and an occa- 
sional duplicated (2) Desmid ; and lines of cells, some of which appear to be 
sparingly., branched. Besides these were found a few Diatomacese. It is ob- 
served for the use of those who undertake the investigation of siliceous 
concretions, that the use of turpentine renders the chips of chert (3) almost as 
transparent as glass. 
Entry of Minute Organisms through tlic Pores of the Body. — Mr. Carter of 
Bombay thinks there is reason to believe that the Guinea-worm is a mon- 
strous development of some minute species of free Filaridae (4), and that these 
little creatures having a calibre much smaller than the ducts of the sudorific 
gland, probably pass through those apertures into the human body. He has 
found them entering thus through the even minuter apertures of a species 
of Sphceria(o). So also the black Fungus disease of India, as he thinks highly 
probable, may arise from the entry in the form of a Zoospore, of a species of 
Mucor(6), through the sudorific ducts. 
Foot of the Fly. — Mr. Tuffen West, in an elaborate article in the Linnaean 
Transactions, has most carefully examined and described this remarkable and 
complicated organ. With regard to the vexed question of the insect’s mode 
of walking back downward on smooth surfaces, he says, “ When a fly is not 
making use of its pulvilli, as on a surface sufficiently rough to afford it foot- 
hold with its claws alone, they only are made use of. On a smooth surface, 
however, perpendicular or horizontal, the pulvilli are brought down, and 
certain tenent hairs (so called because they are the immediate agents in hold- 
ing, and which project from the inferior surface of the flaps at the base of 
the claws), are applied to such surface. A slight push forwards of these, 
succeeded by a gentle draw backwards at each application, removes the air 
between their soft elastic exj>ansions and their plane of motion, and thus a 
firm hold is gained. Access of air is prevented by the minute quantity of 
air which exudes from the expanded tips of the tenent appendages ; and thus 
a vacuum is formed, on the same principle as in the “ Atmospheric Hat-peg,” 
or “ artificial gums ” of the dentist. When the fly wishes to remove a leg 
from its place of attachment, the claws are brought down and pressed against 
the surface ; from their position they raise the hinder part of the pulvillus, 
where the tenent hairs are least developed, first, and so on forward. A fly, 
when once stuck fast, if it had no claws, might remain so. The pressure of 
the atmosphere is thus the main agent which enables the fly to adhere to per- 
fectly smooth surfaces. The atmospheric pressure on the area of the flaps 
alone is calculated at just one-half the weight of the fly, that on the tenent 
hairs at one-fourth more. Mr. West accounts for the remaining fourth by the 
slight viscidity of the fluid (sudor), by grasping, and other delicate and subtle 
agencies. 
Mounting Polyzoa, &c . — The difficulty of showing Polyzoa and Hydrozoa 
with outstretched tentacles, under the microscope, has been overcome by Mr. 
J. W. Morris, of Bath, by adding spirits of wine, drop by drop, to water in 
the cell containing the living animals, which causes them to unfold their 
arms, and in that condition die. Thwaits’ fluid is also recommended. 
