Scientific American Supplement, No. 392, July 7, 1883
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Various >> Scientific American Supplement, No. 392, July 7, 1883
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SPONGES AT THE BAHAMAS.
Within the last few decades the sponge industry of the Bahama Islands
has increased at such a rate that to-day it is the second in importance
on the island. Although the product is not of such excellent quality
as that from the Mediterranean, it sells well and is in demand both in
England and in America.
For sponge fishing little boats of ten tons burden are employed and
manned by from six to twelve men. The sponges that are washed upon the
rocks and reefs are taken with iron rakes fastened to long poles, or
are brought to the surface by divers and spread out on the deck of the
vessel. This kills their soft, slimy organisms, which are black as tar.
The sponges are then repeatedly beaten with sticks to remove this black
slime, and afterward well washed.
The sponges are then sorted and softened for several hours in lime
water, dried in the sun, and bleached. They are finally pressed by
machinery into 100 lb. balls and then packed for shipping.
A rich and very extensive "sponge field" was recently discovered near
Eleuthera, but as the water there has a considerable depth, five or six
fathoms, fishing is attended with difficulty. In fact, it is rendered
impossible wherever the "segler" or sailor fish are found, for the mud
which these tiny creatures stir up completely veils the sponges from the
eye of the fisherman.
In 1881 the export amounted to $150,000, of which three-fourths came to
America.--_Chem. Zeit_.
* * * * *
TESTING FISH OVA FOR IMPREGNATION.
The development of the eyes of game fishes (salmonoids), as is well
known, is relatively far advanced before the fish culturist is
positively assured that embryos are developing normally in the egg.
A method, therefore, which would enable us to shorten this period of
probation would not only be desirable, but be also of value under
certain circumstances, since it is certainly annoying after having had
them in water for four or five weeks, spending time and care over them,
to eventually find, when the "eye spots" do not develop, that all our
trouble was wasted and that no development at all took place.
It is true one may, with proper preparations and with the help of the
pocket lens or microscope, follow the development while there may be no
external signs of the process evident. This method of making the
test is, however, not adapted to the purposes of the practical fish
culturist, who will have better success by the following method:
If fertilized fish ova are placed in a 50 per cent. solution of wine
vinegar [any ordinary vinegar will probably be found to answer just
as well--_Tr_.] the embryo, even during the very first stages of
development, will become apparent to the eye lying on the transparent
yelk. The acetic acid contained in the mixture, one part water to
one part wine vinegar, causes the material of the embryo proper to
coagulate, while the yelk remains clear.
A short time after the ova are laid in this mixture, and during the
first week after impregnation, a white circle at one pole of the
egg should become apparent, and in the course of the second week a
cylindrical white streak running from the edge of the circle toward its
center should be evident. If these features are not developed by the
test, the eggs have not been fertilized, and are, therefore, worthless.
We will not complicate the application of the method by describing other
details of the development, but would merely suggest that when a lot of
ova are fertilized a small portion should be left unimpregnated. These
could then be tested in comparison with the fertilized ova from day to
day, using say three eggs at a time of each lot. The observant culturist
could by this means construct for himself a scale of development
covering the period embraced by his experiments. At a lower temperature
the development is slower than at a higher one. The difference of
appearance between fertilized and unfertilized ova treated by the method
will demonstrate its utility. Whoever does not trust to the method for
the evidence of death of the eggs until after five weeks subsequent to
impregnation, must of course wait.
Director Tiefenthaler, of Koelzen, has had the kindness to test the
method practically, and finds it useful to fish culturists.--_Prof.
Nussbaum_.
[A very little practice, it seems to the translator, would serve to
enable any person of ordinary intelligence to apply this method, or
several others which might be suggested. Other substances which would
answer the same purpose would be dilute solutions of picric or chromic
acid, of not more than one to one-half per cent., or one part to two
hundred of water. Vinegar or acetic acid of the shops may also be used;
the last to be diluted in the proportions of about one part in ten of
water. The acids cited will coagulate and cause the germ disk to turn
white or yellow in a few hours. Chromic is better than picric acid, as
it coagulates the yelk also, but turns the latter much darker than the
embryo or embryonic disk.--_Tr_.]
* * * * *
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papers heretofore published in the SUPPLEMENT, may be had gratis at this
office.
* * * * *
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