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PHYSICAL CHANGES IN THE CONSTITUENT PARTS OF DEVELOPING SALMON EGGS |
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Canadian Journal of Research,
Volume 20d,
Issue 5,
1942,
Page 99-114
F. R. Hayes,
F. H. Armstrong,
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摘要:
Wet weight and dry weight determinations were made on salmon eggs, egg capsules, detached embryos, and yolk sacs from fertilization to the end of yolk absorption. One capsule weighs 5.0 mg. wet and 2.3 mg. dry. No significant change could be found during development. Water hardening of the eggs, which occurs on transfer from coelomic fluid to water, is independent of fertilization. Increased tension of the capsule (resistance to breakage) becomes noticeable two hours after transfer to water and proceeds at a maximum rate for 30 hr. By contrast the uptake of water begins immediately on transfer from coelomic fluid and is virtually completed within an hour. It is concluded that the stoppage of water uptake is not due to the hardening of the capsule. The theory is presented that (a) all the water taken up becomes perivitelline fluid, (b) there is no loss of salt or gain of water by the yolk, (c) the transfer of water through the capsule is not due to osmosis but to imbibition by protein liberated into the perivitelline space by the yolk. The mortality rate for eggs reaches a maximum 14 days after fertilization (i.e., 36 days before hatching). The water content of the yolk decreases steadily during development, from 63.5 to 55.5%. Embryos from small eggs tend to compensate by growing more rapidly than those from large eggs, through the mechanism of extra water uptake. As to efficiency, which proved independent of egg size, the embryo wastes 30% of the yolk in turning the other 70% into living tissue.
ISSN:1923-4287
DOI:10.1139/cjr42d-010
出版商:NRC Research Press
年代:1942
数据来源: NRC
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FIELD TRIALS OF CONTROL MEASURES FOR PARASITIC DISEASES OF SHEEP |
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Canadian Journal of Research,
Volume 20d,
Issue 5,
1942,
Page 115-132
W. E. Swales,
P. E. Sylvestre,
S. B. Williams,
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摘要:
Field tests of methods of helminth parasite control through anthelmintic medication of sheep flocks on the ranges of the Central Experimental Farm, Dominion Department of Agriculture, Ottawa, during 1937, 1938, 1940, and 1941 are described briefly.Some observations on the effects of parasite burdens have been made.Following the development of phenothiazine in 1939 as a practical and highly effective anthelmintic for sheep, medication of adult sheep before the pasturing season was very effective in preventing nodular worm infections in lambs. One early spring treatment in 1940 and a similar one in 1941 reduced the incidence of nodular disease lesions to 0.65 per lamb, a reduction from the figures of 1938 of 99.1% in the lambs slaughtered in the autumn.In spite of no treatment of the lambs during 1940 and 1941,Haemonchus,Monodontus, andCooperiawere reduced to very low numbers and no significant increase in other genera occurred.It is suggested thatOesophagostomumhas been reduced to a level too low for subsequent recovery in these flocks unless it is reintroduced in new stock; thus this parasite can be considered as probably eradicated.
ISSN:1923-4287
DOI:10.1139/cjr42d-011
出版商:NRC Research Press
年代:1942
数据来源: NRC
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