. Anatomischer Anzeiger. L'anatomie, l'Anatomie Comparée ;, comparatif. 231 en ce qui concerne l'embryon de la grenouille est concerné tombe au sol. Hert- la perruque preuve tératologiques (spina bifida cas-si convaincante pour beaucoup d'esprits) est purement circonstancielle, et par lui-même est ainsi ex- plained sur l'hypothèse d'une rupture, dont on suppose de progresser peu à peu la lèvre dorsale pendant le mouvement de ce lèvre vers le pôle inférieur, comme elle l'est par la concrescence théorie. La très instructive pendant de la spina bifida embryon, il me semble, est d'être trouvés dans les embryons comme Hertwig ('93, '95

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. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 231 as far as the frog embryo is concerned falls to the ground. Hert- wig's teratological evidence (spina bifida cases—so convincing to many minds) is purely circumstantial, and by itself is as well ex- plained on the hypothesis of a rupture, which we must suppose to progress gradually away from the dorsal lip during the motion of that lip towards the lower pole, as it is by the concrescence theory. The very instructive counterpart of the spina bifida embryo, it seems to me, is to be found in embryos such as Hertwig ('93, '95) has reared in werk salt solution. In the latter it is the ventral wall which is ruptured instead of the dorsal, the rupture passing poster- iorly into the true blastopore. 1. Ovate produced in the centre of the black hemi- s p h e r e. Experiment 1. On March 19, at 1.45 P.M., 13 Amblystoma eggs in a late stage of segmentation were pierced as nearly as pos- sible in the centre of the black hemisphere — the position of the ovate is shown in Fig. 16', a side view of the egg. The eggs were. placed on a mirror and covered with water. The ovates in the natural position of the egg were not easy to see. Careful examination showed however that in only three out of the thirteen eggs, was the ovate perceptibly out of the centre of the upper hemisphere — and in these three eggs the distance from the centre was slight. — The blastopore came in at 10 P.M., appearing through a lens as an actual cleft in the white hemisphere. The next morning at 11 A.M. it was circular, . Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Anatomische Gesellschaft. Jena : G. Fischer

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