. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NUCLEOLI IN PEDICELLINA AMERICANA. 349 floor of the atrium and there multiply very rapidly. This in- crease is much more pronounced in the male than in the female and gives the first and principal basis for the distinction now present between the sexes. The bi-partite testis, with its sperma- togonia, has grown considerably and the latter are mostly in the resting condition. The nuclei are large, being surrounded by a very thin layer of cytoplasm. Within the nucleus, the chroma- tin, in the form of a reticulum, stains very l
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NUCLEOLI IN PEDICELLINA AMERICANA. 349 floor of the atrium and there multiply very rapidly. This in- crease is much more pronounced in the male than in the female and gives the first and principal basis for the distinction now present between the sexes. The bi-partite testis, with its sperma- togonia, has grown considerably and the latter are mostly in the resting condition. The nuclei are large, being surrounded by a very thin layer of cytoplasm. Within the nucleus, the chroma- tin, in the form of a reticulum, stains very lightly ; indeed, in well extracted iron-haematoxylin preparations shows scarcely at all. But what is more important is the almost invariable presence of the one or the two nucleoli. These stain uniformly and in- tensely black with hasmotoxylin and retain their color long after that of the other cell elements has been extracted. When in pairs, they are placed at opposite points of the nucleus ; when single, the nucleolus is found more nearly in the middle. The cells of the other tissues have preserved the same condition of the nuclei as was above described for the younger polyp. In older testes, many more cells are present (Fig. 2), and these are proved, by the unreduced number of the chromosomes, to be also spermatogonia. Among these are cells of many sizes both. FIG. 3. at rest and in mitosis from which it is certain that there are several generations of spermatogonia. In tracing the development of the spermatogonium from the telophase of the preceding division, attention is attracted by the appearance of the two nucleoli. At the beginning of the reconstruction there is as yet no trace of them. This stage is soon followed by one where the nuclear membrane has reappeared, the chromatin being almost entirely unaffected by haematoxylin. At two opposite points of the nucleus there now appear the two nucleoli as yet very small but. Please note that these images are extracted from s
Size: 2616px × 955px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
