Abstract
THE PROGRESS OF EMBRYOLOGY.—The value of Dr. Dohrn's Zoological Station at Naples has never been more conclusively demonstrated than by the publication, in a recent number (July, 1876) of the Archiv für mikroskopische Anatomie, of a series of researches by Dr. Bobretzky, of Kiew, on the development of certain forms of Gastropods. The systematic search for embryonic forms which is carried on under Dr. Dohrn's superintendence lias enabled. Dr. Bobretzky to publish a memoir of great value, illustrated by a hundred figures. His skill and success have been previously attested by his excellent researches on the development of the crustacean genera, Astacus, Palæmon, and Oniscus; and he has now passed with equal good fortune into the Gastropod group, dealing with the genera Nass, Natica, and Fusus. These investigations are of special interest because, according to Prof. Ray Lankester, they are the first in which the method of cutting sections has been employed in the examination of these minute eggs and embryos. To have carried the conquests of embryology to such an extent is no slight achievement. Histologists are well aware that the estimate formed of structures by viewing them as transparent objects is liable to be erroneous, even in favourable circumstances; much more so when the objects have an appreciable thickness and are more or less opaque. In all cases it is desirable to obtain, if possible, confirmatory evidence by means of sections cut through hardened specimens; but the labour and manipulative skill required are much greater than in viewing bodies as transparent objects. At the same time Dr. Bobretzky's results convey an instructive warning to those who are tempted to generalise. Nothing is more common, or more detrimental, than for a series of generalisations to be founded on a new set of observations more or less limited in their range. By the con. tinual discovery of fresh variations in the mode in which the ova of aquatic animals are segmented, and acquire their embryonic layers, it is to be hoped that students are being led to see that nothing but summaries of observed facts are of real value at present. Dr. Bobretzky seems to have made it evident that in the genus Nassa the three primary embryonic layers are all established during the segmentation of the ovum, and as a direct result of that process; and this is certainly a surprise. Again, a definite relation has been made out in certain; cases between the orifice of the earliest invagination of cells and the permanent mouth of the animal. It is to be regretted, however, that Dr. Bobretzky throws doubt on Prof. Lankester's observations on some genera of fresh-water Gastropods, in which facts of a different character were discovered. However, the latter investigator has been stimulated to examine the development of the common Paludina vivipara anew, and has published an account of it in the Quarterly Journal of Microscopical Science for October last; his previous assertions appear to be very definitely confirmed, notwithstanding that the method of sections has not been adopted: the embryos, it may be stated, are amongst the most transparent in the Gastropod class. Although it must be a disappointment to ardent theorists to find that they are so far from a satisfactory goal, it may encourage young workers when it is seen that the field for independent investigation, is practically unlimited, even in embryology. In invertebrates, at least, it appears that the development of every genus should be studied and that new facts bearing on evolution, on the distribution of life, on the influence of external conditions, on the warping, so to speak, of the direct process of development by temporary influences acting during embryonic life, will reward all diligent work in this fruitful field.
Article PDF
Rights and permissions
About this article
Cite this article
Biological Notes. Nature 15, 65–67 (1876). https://doi.org/10.1038/015065b0
Issue Date:
DOI: https://doi.org/10.1038/015065b0