Henry Baldwin Ward
Published: 2013-09
Total Pages: 48
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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 edition. Excerpt: ...II. A. 1. in case migrations of large numbers of individuals occurred only vertically. This condition would yield equal volumes for equal bottom hauls but unequal volumes for some other equal hauls. b. Or arranged without reference to each other so that vertical columns of water of equal dimensions and extending from surface to bottom will usually contain unequal volumes of plankton in different parts of the lake. This would result from I. or II. A. 1, by migration of masses of individuals horizontally or obliquely. Such migrating masses may produce local accumulations of any conceivable form or size, such as spheres, sheets extending horizontally or vertically, etc. They are thus capable of producing a wide range of variation in the volume of the plankton from bottom and other hauls. The migrating masses may consist of all the species existing in the plankton and in the proportions in which they exist there--in which case the resulting local accumulations may be called plankton swarms; or they may consist of one or several species and might be called species swarms. Species swarms occurring in such way as to compensate one another would remain undetected by the volumetric method." The work of the first day with the vertical net was experimental, and does not show any uniformity in the number or depth of the various hauls at each station, as given in the table, page 32. They cannot be used for this reason in the comparative study of the strata. In all hauls thereafter distinguished a number of artificial strata as follows: 1. A surface stratum from 2 m. to the surface. we 2. 3. 4. 5. 6. 7. An intermediate stratum from An An A deep A" A" 5 in. to 2 m. "10"" 5" "25" " 10" "50..".
