. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HYDROZOAN EXPERIMENTAL EMBRYOLOGY 607 parts show the correct proportions (Fig. lOe). However, in half of these cases the nectophore was smaller than normal and nonfunctional or rudimentary (Fig. lOd). Since many of these oral isolates with a nectophore have a corresponding aboral isolate from the same embryo that has also formed a nectophore, the oral isolate must have formed a nectophore as a consequence of a regulatory adjustment that occurred as a result of the operation. Between 15 and 22 hours of development there is a
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. HYDROZOAN EXPERIMENTAL EMBRYOLOGY 607 parts show the correct proportions (Fig. lOe). However, in half of these cases the nectophore was smaller than normal and nonfunctional or rudimentary (Fig. lOd). Since many of these oral isolates with a nectophore have a corresponding aboral isolate from the same embryo that has also formed a nectophore, the oral isolate must have formed a nectophore as a consequence of a regulatory adjustment that occurred as a result of the operation. Between 15 and 22 hours of development there is a marked decrease in the ability of the oral halves to differentiate a nectophore. These cases form a tentacle at their anterior end and a posterior mouth (Fig. 100- These experiments show that in both the Muggiaea and Nanomia embryos there is an early specification of the ways in which the different regions will differentiate along the oral-aboral axis of the future larva. However, in Muggiaea differentiation of part of the oral region of the embryo can be respecified until just before the first indications of organogenesis. 2) Since the different regions along the oral-aboral axis of the Nanomia embryo appear to be specified some time before the eight cell stage, an attempt was made to bracket the time period when specification occurs. Eggs which were undergoing their first cleavage (14 cases) and two cell stage embryos that were marked at the site of first cleavage initiation (5 cases) were cut into oral and aboral halves (Fig. 11). In each case only the oral half contained the nuclei, and thus it was the only half that developed. When an operation was done the diameter of each fragment was measured to calculate the relative volume of the oral isolate. The results of these experiments are presented in Table III. Unlike the oral isolates produced at the eight-cell stage and at later stages, a substantial proportion of these cases formed large vacuolated cells and a pneumatophor
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
