NATURE 



52Q 



THURSDAY, APRIL 9, 1908. 



EXPERIMENTAL EMBRYOLOGY. 



Experitnental-Zoologie. Part i. Embryogenese. Eine 

 Zusamnenfassung der durch Versuche eimittelten 

 Gesetzmassigkeiten tierischer Ei-Ent\vicklung 

 (Befruchtung, Furchung, Organbildung). By Dr. 

 Hans Przibram. Pp. 125; 16 plates. (Leipzig und 

 Wien : Franz Deuticke, 1907.) Price 7 marks. 



SOME three years ago Dr. Przibram, who is well 

 known as a brilliant representative of the school 

 of experimental zoologists, published " An Introduc- 

 tion to Experimental Morphology," which met with 

 wide acceptance. The present volume is an expansion 

 of part of the " Introduction," and forms an inde- 

 pendent treatise on experimental embryology. It is 

 to be followed by four other parts, dealing- with 

 regeneration, evolution, vitality, and function, and 

 the whole will form a text-book of experimental 

 zoology. If the subsequent parts are like the one 

 before us in lucidity and thoroughness. Dr. Przibram 

 will earn the gratitude of all interested in this dynamic 

 aspect of the science; and who, nowadays, can afford 

 to stand aloof? The present volume discusses, in the 

 light of experimental results, the processes of fer- 

 tilisation, cleavage, gastrulation, and differentiation, 

 and sums up in an analysis of the influence of chemical 

 stimuli, moisture, density of the medium, pressure, 

 gravity, electricity and magnetism, light and heat. 

 There is a copious and carefully executed bibliography, 

 and the figures in the plates, which are partly com- 

 piled and partly original, are very clear and interest- 

 ing. 



The author discusses large and difficult problems, in 

 regard to which there is room for considerable differ- 

 ence of opinion, but his treatment of these is 

 thoroughly objective and undogmatic. We cannot do 

 better than give some samples of his general con- 

 clusions. Fertilisation, whether artificial or spermatic, 

 brings about a withdrawal of water from the egg ; this 

 accelerates the vital processes which are going on of 

 themselves, and the egg passes from a relatively 

 resting state to progressive development. The un- 

 fertilised egg has an organisation of different kinds 

 of substances which guarantees the forthcoming mani- 

 foldness. The direction of the first cleavage is in a 

 plane at right angles to the axis of the first karyo- 

 kiiietic spindle, and the position of the latter is deter- 

 mined by the geometrical architecture of the egg and 

 the fertilisation-meridian (on which the spermatozoon 

 enters). 

 L In regard to the familiar sequence of centrosome 



I division, astrosphere formation, nuclear division, 

 cytoplasmic division, and perhaps also the progressive 

 differentiation of the blastomeres, we must not suppose 

 that any particular link in the chain is the necessary 

 cause of the next link ; we must rather suppose that 

 a common cause evokes them in succession, and that 

 their cooperation secures the typical development. 

 Provisionally we may say that the common cause of 

 the mitotic phenomena lies in a localised change in 

 NO. 2006, VOL. 77] 



the fluidity of the enchylemma and the associated re- 

 arrangement of a monocentric into a dicentric surface- 

 tension-system. The second and subsequent cleavages 

 depend on a rhythmic recurrence of the metabolic rela- 

 tions involved in the first cleavage (the entrance of 

 oxygen conditioning the continuance of the meta- 

 bolism, the intensity of which changes with the 

 changes in the proportion of absorbent surface to 

 assimilatory volume), and on the presence of an- 

 tagonistic substances, which partly prevent the com- 

 plete separation of the blastomeres (calcium), and 

 partly secure a certain cohesion (sodium). 



The arrangement of the blastomeres depends on 

 Plateau's law of the smallest surface, modified bv 

 differences in the consistence of different parts of 

 the ovum, which are also responsible for the different 

 sizes of the blastomeres (Balfour's law). Blastulation 

 and gastrulation depend on chemotactic influences, 

 which are set at work by metabolic processes, and 

 admit not only of passive-mechanical displacements, 

 but of active migrations as well. In different zones 

 of the egg there are chemically different substances 

 which normally condition the differentiation of the 

 various organs. Thus the blastomeres acquire a pro- 

 spective value. If there is no rearrangement of 

 material, an artificial fractioniny of the egg is 

 followed by a self-differentiation of the fragments, so 

 that semi-embryos, quarto-embryos, and so on, 

 result; but if a re-arrangement is effected, restoring 

 the status quo of the intact ovum, then dwarf com- 

 plete embryos result. The prospective potency of such 

 blastomeres is greater than their prospective value. 

 The influence of external factors is subsidiary when 

 compared with the internal formative factors, and 

 animal embryogenesis may be described as an almost 

 quite perfect self-differentiation in Roux's sense. 



We have stated these general conclusions because 

 of their great interest, but it must be noted that 

 the bulk of the book is a terse statement of concrete 

 facts from which the expert student may draw his 

 own conclusions, and at this stage that is well. 



J. A. T. 



GEOLOGICAL REVIVALISM. 

 Gcologische Prinzipienfragen. By E. Reyer. Pp. 

 X + 202. (Leipzig: W. Engelmann, 1907.) Price 

 4.40 marks. 



THIS work recalls, with renewed interest, a 

 remarkable paper by Mr. Reyer on the Schloss- 

 berg of Teplitz, to which the attention of the present 

 writer was directed by Prof. Judd nearly thirty years 

 ago. Are not some of Reyer 's models still preserved 

 in London, and have not these models, and respectful 

 visits to the Schlossberg itself, influenced many of us 

 in our attempts at teaching ever since ? Mr. Reyer, 

 however, when he went further into the theory of 

 the formation of mountains by the protrusion of 

 masses from below and the gliding of the superin- 

 cumbent layers, found the geological world opposed 

 to him, and he turned, as he now informs us (p. v.), 

 to fields of sociological activity. Yet he should surely 

 be satisfied with the numerous references to his 



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