Vol. XXIV. No. ii.] 
POPULAR SCIENCE ITEWS. 
171 
progress was made. In two days the founda- 
tion was laid, and the next day the frame was 
raised and tlie boards nailed on. Unfortu- 
nately, three of the workmen had already 
succumbed to the " mountain sickness" and 
returned to the valley, while a threatened 
storm rendered it necessary for the whole 
party to follow them. M. Vallot had brought 
with him a bag of oxygen gas, and it was 
found that inhalations of this were of great 
service in overcoming the weakness and pros- 
tration due to the rarefied air of the high 
altitude. One of the workmen was so com- 
pletely overcome that he was unable to move, 
and would, perhaps, have perished but for 
the aid given by this stimulating element. 
On the 31st of July, the storm having 
passetl, the party, accompanied by Mr. Law- 
rence Rotch, of the Blue Hill Observatory, 
near Boston, returned to the mountain, and 
completed the building, by covering the 
planks with tarred felt, erecting a lightning- 
rod, and strengthening the walls by heaping 
stones around them. On the 2d of August 
the work was completed, and the next da}- 
the party descended to Chamonix, where they 
received a most enthusiastic ovation. 
On the 17th of August, M. Vallot, with 
MM. Janssen and Durier, spent three days 
in the observatory, where they were detained 
by a terrible storm, which the building with- 
stood without injury. The wind was esti- 
mated to blow at the rate of over 200 miles 
ari hour. The barometer varied a quarter 
of an inch within two minutes, and every- 
thing in the camp outside — including two 
camp bedsteads and a can of oil — was blown 
completely oft" the mountain and carried to 
great distances. 
Both mountain-climbers and scientists owe 
a debt of gratitude to M. Vallot, through 
whose enterprise this station has been erected, 
which will not only add much to the safety 
and comfort of future visitors to the summit, 
but will undoubtedly greatly increase our 
knowledge of the meteorological conditions 
of these elevated and often inaccessible re- 
gions. 
«♦► 
TitE sun's distance, as stated by Prof, llarkness, 
an American member of the Transit of Venus 
Commission, is 92,455,000 miles from the earth, 
with a probable error of 123,400 miles. 
fOriginal in Popular Science News,] 
BRIEF STUDIES IN BIOLOGY. 
BY PROF. JAMES H. STOLLER. 
VI. 
THE SNAIL. 
The sixth sub-kingdom of animals (and the last 
of the primary division Interiehrdta) is the Mollusca. 
The word is derived from the Latin mollis, soft, and 
has reference to the soft, fleshy bodies of these 
animals, leaving out of account the exterior shells 
possessed by most members of the group. The 
most commonly known molluscs are the snail, slug, 
oyster, clam, mussel, etc. For our study we choose 
the snail, as a representative molluscan animal, and 
one that can everywhere be easily obtained for 
examination. Any common species — whether of 
those living in water and so abundant in all ponds 
and streams, or those found on land — is suitable for 
observational study. 
We may begin by noticing the most striking 
external feature, the shell. There is no class 
of animals which have a more perfect protective 
armor than the snails. In the combat for existence, 
which is the common lot of all living things, and 
has been in all time past, the manner of warfare 
among the snail tribe has been solely one of defense ; 
and they have come to possess, as an outcome of an 
evolution toward the perfect, an armor of defense 
that is without defect. It is not surprising, there- 
fore, that the snail class has fared well in the race 
for existence, and has been, since early geologic 
times, one of the most persistent types of animals. 
The shell consists of carbonate of lime, and is 
formed by secretion from a portion of the integu- 
ment called the mantle, receiving this name from 
the fact that it surrounds the internal organs. The 
shell grows by additions at the mouth, so that the 
oldest part is at the summit, or apex, of the spiral. 
If the shell becomes broken, the snail mends it by a 
fresh secretion. At the approach of winter the 
animals creep into the soft earth, and, having drawn 
their bodies into the shell, secrete a thick fluid, 
which hardens into a firm crust that closes the 
mouth of the shell. This crust is permeable to air, 
so that snails carry on — like all animals that hiber- 
nate — a reduced respiration during the winter. 
Passing now to the examination of a living snail, 
as the animal appears while in the act of creeping 
about, it is to be observed that there is a distinct 
head-end to the body ; that is to say, there is an 
anterior portion, at which the mouth is situated, 
and which bears sense-organs. If it is the common 
land-snail {Helix albolabris) we are examining, two 
pairs of organs of sense will be noticed. These are 
the tentacles, commonly called the " horns," serving 
as organs of touch, and a pair of eyes, borne at the 
ends of stalks. Further evidence that the snail is 
entitled to be ranked as a cephalous, or head-bearing 
animal, is afforded by dissection, which shows the 
presence of a mass of nerve-ganglia at the anterior 
end, above the gullet, from which pass out nerves 
to the tentacles and the eyes. While it is objection- 
able to call this mass of nerve-cells the brain, since 
the term connotes a mentality higher than that 
which can be ascribed to the snail, it yet corresponds 
in general position and — it can scarcely be doubted 
— in functions, as the seat of sensations, to this 
organ in the higher animals. We shall not err in 
saying that snails are animals of a high order 
of development — surpassed only by those possessing 
a vertebral column and dorsal nervous system, form- 
ing the great sub-kingdom Vertehraia. The snails 
are markedly higher in organization than molluscs 
of the type of the mussel or clam, whose bodies 
show no difterentiation into a head and posterior 
region. - 
The manner in which locomotion is eflfected by 
the snail is worthy of notice. It will be observed 
that it possesses a broad, fleshy, creeping-disc, and 
that by muscular movements, taking place from 
before backward, the body is slowly dragged along. 
The integument of the disc is supplied with numer- 
ous secreting glands, which discharge a slimy'fluid, 
the use of which appears to be to lubricate the sur- 
face over which the animal is creeping. 
Further examination of the living snail is difficult, 
because, upon being handled, the body is immedi- 
ately withdrawn into the shell. But a living snail 
can always be made to crawl out of its shell by 
placing it in water which has been boiled, and thus 
deprived of the air contained in it. The jar con- 
taining the water should be covered, otherwise the 
snails will simply crawl to the surface and get air 
there. After the animals have become partially 
stupefied,— and it is not likely the process causes 
them much pain, — they may be quickly taken from 
the water and plunged into boiling water. In this 
way they are killed, and with the body extended. 
Further study can then be made. 
The mouth may be seen at the anterior end of the 
creeping-disc. Just within the lips, and forming 
the roof of the mouth, is a strong, ridged plate, 
composed — like the shell — of carbonate of lime. 
This plate works backward and forward over a 
hard, gristly cushion, which forms the floor of the 
mouth. In this way the food, which consists 
of vegetable matter, is made ready for passage 
into the alimentary canal. To trace the course 
of the alimentary tr.ict, dissection is necessary. It 
will be found to extend a considerable distance into 
the spiral cavity of the shell, and then, turning 
upon itself, to pass outward, and open upon the 
upper side of the body. Connected with the diges- 
tive canal, and extending into the narrowest portion 
of the shell, is a large, dark-colored organ, called 
the liver. 
Snails possess definite organs of breathing, but 
the lung of the land-snail is an organ as simple as 
can be conceived. It consists simply of a chamber 
formed by an in-folding of the skin. A small open- 
ing affords the passage of air, in and out. The 
walls of the chamber are ramified by blood-vessels, 
and thus respiration — the exchange of carbonic acid 
from the blood for oxygen of the air — is brought 
about. There are some water-snails whose organs 
of breathing are gills, quite analagous to those 
of fishes, but simpler in structure. 
It is clear enough why snails inhabiting water 
need organs of respiration of a higher type of 
structure than the simple air-cavity which con- 
stitutes the lung of the land-snail. To take up 
from water the relatively small quantity of oxygen 
dissolved in it, requires a much larger absorbing 
surface than to withdraw from air free oxygen 
existing in large proportion. We have in this an 
admirable instance of adaptation of organs to their 
environment. And we always find, when we com- 
pare animals belonging to the same zoological order 
but having different habitats, that the generic 
features of structure are maintained in both, but 
secondary features differ in adaptation to their dijfer- 
ent environments. Thus, in this case, the land and 
water-snails have essentially the same bodily struc- 
ture, excepting as regards the organs of respiration, 
and these are in adaptation to the natural medium 
which forms their environment. From instances 
like these may be deduced a biological law of wide 
application : Organs performing the same function 
in different animals vary in structure according to 
the nature of their environments. 
Reference has been made above to the blood- 
vessels of the snail. The animals of this class 
possess a true blood-circulatory system, consisting 
