. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. TEST MATERIAL AND FISSION IN PONTIGULASIA 145 Zuelzer (1904). The vacuoles in the cytoplasm protruding from the shell are pockets from which the sand grains have been dissolved. Fig. 1, />, shows an animal which was fixed just after the collection of shell materials had been completed but before the new shell was formed. The nucleus in this animal is in middle prophase, showing the chromatin granules on a definite linin reticulum. At this stage the nucleus is much enlarged. This section also shows the details of the shell
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. TEST MATERIAL AND FISSION IN PONTIGULASIA 145 Zuelzer (1904). The vacuoles in the cytoplasm protruding from the shell are pockets from which the sand grains have been dissolved. Fig. 1, />, shows an animal which was fixed just after the collection of shell materials had been completed but before the new shell was formed. The nucleus in this animal is in middle prophase, showing the chromatin granules on a definite linin reticulum. At this stage the nucleus is much enlarged. This section also shows the details of the shell very clearly. The internal diaphragm can be seen with the cytoplasm flowing through it. This diaphragm is easily overlooked in the living condition and the constriction between the neck and the. ;i EtAViX- ''*'' .••,S:".-" * FIG. 1. Sections of Pontigulasia vas fixed while gathering test materials before division. Camera lucida drawings. X 400. a. This animal had been collecting fine sand grains for 4 hours. The shell in this section was distorted when sectioned. Note that the nucleus is scarcely changed from the resting condition. b. Section of an animal which had been collecting for 4^ hours. The formation of pseudopods had ceased but the sand grains were still a formless mass in front of the mouth of the old shell. The nucleus is much enlarged and shows a definite linin reticulum with the chromatin granules. Middle prophase. Note the constriction and the internal diaphragm in the shell. fundus is not as deep in these forms as described by Penard (1902), Cash (1909), and Kudo (1931). The process of division was not investigated further in this study, but it seems fairly certain that nuclear division is not started until the collecting of shell materials has been completed. A more complete study of binary fission in this form is being made. DISCUSSION As far as these experiments on the control of division in Ponti- gulasia vas were carried, it seems that repr
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
