Publisher's Synopsis
Excerpt from A Study of the Chromosomes of the Germ Cells of Metazoa: Read Before the American Philosophical Society, January 18, 1901
In the present paper the part containing the general conclusions may appear dispro portionally great to the record of the observations. These observations are to great extent on the number and valence of the chromosomes and chromatin nucleoli from the time of the last generation of the spermatogonia up to the formation of the spermatids. But the determination of these numbers is very difficult; large numbers of sections have to be examined in order to'find the necessary stages, and the number of the chromosomes of each stage have to be counted in a considerable number of cells of each species in order to insure accuracy. The counting has been done in all cases by selecting those cells in which the chromosomes are most loosely grouped, being sure at the same time that all the chromosomes are in the plane of the section, drawing the chromosomes carefully with the camera lucida, then counting their number on the drawings. This demands much patience and time, necessitating also constant re'e'xaminations and study of new material, though the results may be tabulated in a very small space. Of course the difficulties are most pronounced where the chromosomes are numerous and small.
The material was collected by me at two localities - ih the vicinity of Philadelphia, Pennsylvania, and in the neighborhood of Wood's Holl, Massachusetts. Great care was taken to insure accurate identification of the species, and my specimens were directly compared by me with the collections in the museums of the Wagner Institute of Science and of the Academy of Natural Sciences of this city; these collections had been labeled by Dr. P. R. Uhler, of Baltimore, our foremost American authority on this group of Insects; and I must also acknowledge my indebtedness to Dr. Uhler for kindly identify ing a number of species which were not represented in the collections just mentioned. To my friend, Mr. C. W. J ohnsou, curator of the Wagner Institute, my thanks are also due for aid in identification. The differences of the spermatogenetic phenomena of different species shows how important it is to secure accurate identification.
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