June 8, 1876J 



NATURE 



13; 



SCIENCE IN GERMANY 



{From a Gerfnan Correspondent^^ 



TOURING the past year some interesting observations 

 ■*-^ have been published with reference to the altera- 

 tions in animals through external influences. One series 

 of these researches is by Weissmann, on the transforma- 

 tion of the Mexican Axolotl into an Amblystoma {Zeit- 

 schrift fiir Wissenscha/iliche Zoologie,xxv., 1875, Supple- 

 ment). It refers, of course, to a phenomenon which is 

 not now new ; but it includes a number of original experi- 

 ments and observations, and is especially important for 

 the conclusions drawn from these. The Axolotl {Siredon 

 Mexicatiiis) and its allies in Mexico retain there, during 

 life, in the natural state, the form and organisation of the 

 larvas of our Tritons ; but, in artificially breeding them 

 in Europe, they sometimes undergo a metamorphosis into 

 an Amblystoma, i.e. an animal of the form of our fully 

 developed Tritons. These peculiar departures from the 

 natural behaviour of the Mexican Siredon, Weissmann 

 desired to produce artificially, and with this view he en- 

 trusted the breeding of five eight-day larvae to a lady, 

 Fraiilein v. Chauvain. All five actually underwent the de- 

 sired transformation, having been put for six toeight months 

 in water that was quite shallow, so that they were compelled 

 frequently to leave the water, and become used to lung- 

 breathing. Now, since, besides the Mexican Siredon 

 species, which are never transformed in the natural state, 

 there occur in the United States of North America quite 

 similar animals, which, however, represent merely the 

 temporary larva stage of various species of Amblystoma, 

 the Mexican Siredon species have hithertobeen regarded as 

 forms that have remained at a lower stage of development, 

 and, in the rare cases of metamorphosis by the action of 

 changed conditions of life, have been incited to progres- 

 sion towards a higher stage. Weissmann, however, is now 

 of a different opinion. He believes that the sudden 

 and very remarkable transformation of the Siredon, 

 which affects a whole series of organs, cannot be fully 

 explained by the direct influence of changed conditions 

 of life ; and that should one see in such a transformation 

 the leap-like {sprunj^weise) development of a new species 

 or even genus, the hypothesis of a kind of life-force would 

 be necessary. This teleological hypothesis should be 

 avoided, according to Weissmann, and the transforma- 

 tion of the Siredon conceived as a not real but only appa- 

 rent new formation of species, viz., as a reversion to a 

 form which previously existed among the ancestors of the 

 Siredon. Since the Pejrennibranchiata, at all events, re- 

 present the older form of the tailed amphibians, as it is indi- 

 cated for the Amblystomas of North America in their Sire- 

 don-like larvae, all Siredons are to be regarded as the 

 descendants of Amblystomas, which were permanently 

 depressed to that older form, and in their occasional 

 metamorphoses have realised a reversion to the second 

 phylogenetic stage (Amblystoma). Such a conception 

 Weissmann supports by the following reasoning : — The 

 possibility of Siredon having come from Amblystoma is 

 proved by the fact that we sometimes see Triton-larvaa, 

 which attain the full size and sex-forms of an adult Triton 

 without being transformed ; now the Tritons and Ambly- 

 stomas are very similar animals, and their larvae are again 

 extremely similar to the Siredon. But it is possible also 

 to indicate the probable causes which forced the Ambly- 

 stoma-like ancestors of the Siredpn to reversion into the 

 Perennibranchiate form. According to Humboldt's view, 

 the high table-lands of Mexico were formerly covered 

 with extensive lakes, and the evaporation of such large 

 water-surfaces must then have produced a very moist 

 atmosphere, which is necessary to the naked amphibia 

 livtag on land. Consequently, Amblystoma forms could 

 at that time live in Mexico quite well. With disappearance 

 of the waters, however, came the present extreme dryness 

 of the air on the Mexican highlands, which allows only 



the Amphibia living in water to survive, and is therefore 

 probably the reason why the Amblystoma larvae have 

 gradually quite ceased leaving the water and being trans- 

 formed, and thus have constituted the present Siredon 

 species. If, then, the occasional transformation of Siredon 

 to Amblystoma may be explained as a reversion, the 

 necessity ceases of supposing for so sudden a change a 

 special life force, which in Weissmann's opinion is neces- 

 sary, should his theory be rejected. 



Similar experiments on the change of organisation 

 through action of external influences have been made by 

 Scbmankewitsch on low Crustaceans of the order of 

 Branchiopoda. He also was led to experiment by natural 

 occurrences. In the neighbourhood of Odessa (in Southern 

 Russia) there is a salt lake which, with a view to salt 

 production, was divided by a dam into two halves, so that 

 in the lower, shut off part, salt was deposited in solid 

 form, while the less salt upper portion alone, at the com- 

 mencement, contained the Branchiopod Artetnia salina 

 in large number. In the year 1871 that dam burst ; the 

 very salt water of the lower half of the lake was diluted to 

 about 8* of Baiime's areometer, and at the same time there 

 were carried into it large masses of Ariemia salhia. After 

 the dam was repaired the concentration of the same 

 water rose in 1872 to 14°, 1873 to 18", 1874 to 25°. At the 

 same time the Artetnia salina present underwent a re- 

 markable change. In 1871 they still had their charac- 

 teristic form of tail. In 1874 the two lobes of it, as 

 also their bristles, had entirely disappeared. Simul- 

 taneously the gills were enlarged, in correspondence to the 

 smaller proportion of oxygen in the very salt water. The 

 body as a whole, however, decreased in size, so that the 

 new form corresponded almost exactly to that of Artemia 

 Miihlhausenii, formerly regarded as a distinct species. 

 This fact was tested experimentally, and the same results 

 were obtained by artificial breeding in salt water of in- 

 creasing degrees of concentration. Further, by the 

 reverse experiment, the Artemia Miihlhausenii was, even 

 in a few weeks, altered in the direction of Artetnia salina j 

 and this last form was, by continued dilution of the salt 

 water, transformed into a Branchipiis ; i.e. a genus which, 

 of larger dimensions than Artemia salina, has a some- 

 what different tail, and one abdominal segment more, and 

 which also is propagated sexually, whereas partheno- 

 genesis is the rule with Artemia. In natural water-pools,, 

 with various proportions of salt, Scbmankewitsch found 

 (in accordance with his experiments) various traiisition 

 stages between the forms named, so that the increase of 

 the amount of salt reduces the Branchipus form in size, 

 segmentation, and initial form of the post-abdomen, and, 

 with corresponding change of the gills, essentially modi- 

 fies also the propagation, so that the strongest sale 

 solutions harbour only Artemia MiiJilhausenii. From all 

 these facts it appears that the direct influence of changed 

 conditions of life may, in course of a few generations, 

 transform one species, or even one genus, into another, 

 and this in both directions ; so that there can be as little 

 question of the reality of a reversion as of that of im- 

 perceptible small changes, which, accumulating through 

 long periods of time, suffice for the formation of a new 

 form. Such facts, however, seem little fitted to give 

 support to the opinion of Weissmann, viz., that rever- 

 sion only is capable of working a rapid and remarkable 

 change. 



SIEMENS* ELECTRIC LIGHT APPARATUS 



THE comparatively infrequent employment of electric 

 light, considering the great success achieved in its pro- 

 duction, would at first sight appear to be due to something 

 in the application of the electricity itself. It has been re- 

 peatedly and satisfactorily proved that a continuous and 

 powerful light can be produced by electricity, and the 



