October 21, 1898.] 



SCIENCE. 



559 



highly commended to all those who are in im- 

 mediate contact with childhood in the function 

 of director of any sort. 



M. V. O'Shea. 



University of Wisconsin. 



BiomecJianik, erschlossen aus dem Principe der 



Organogenese. Ernst Mehnert. Jena, G. 



Fischer. 1898. Pp. 177. Mk. 5. 



The work hefore us has two purposes : first, 

 to set forth additional evidence for the ' Principe 

 der Organogenese,' already enunciated in the 

 author's work on ' Kainogenesis als Ausdruck 

 diflferenter phylogenetischer Energieen,' 1897; 

 and, secondly, to apply this principle to organic 

 evolution. As one can imagine from the ground 

 covered, the work is one of those more or less 

 interesting webs of speculation which even 

 some of the trained German naturalists are fond 

 of spinning at great length. 



The principle of organogenesis is thus stated 

 by the author : The rapidity of the onto- 

 genetic process of unfolding of an organ 

 is proportional to the height of phylogenetic 

 development which it has attained at the time. 

 It uniformly increases with the elevation above, 

 and uniformly diminishes with the relinquish- 

 ment of, a once attained height of development. 

 The meaning of this principle may be made 

 clearer by a few examples. According to the 

 law of recapitulation of phylogeny iu ontogeny 

 we should expect a phylogenetically older 

 organ to appear in ontogeny before a phylo- 

 genetically younger one. Thus, the great 

 blood vessels of the vertebrate body are doubt- 

 less phylogenetically older than the heart and 

 we should expect them to arise before it. But, 

 on the contrary, the heart, because it has at- 

 tained a higher development than the blood 

 vessels, unfolds in ontogeny first. Its formation 

 has been accelerated. On the other hand, the 

 pineal eye, which is probably derived from that 

 of Tunicates and is, consequently, older than, or 

 at least as old, as the paired eyes, arises in ontog- 

 eny later than the paired eyes. Its unfolding 

 has become retarded since the organ has be- 

 come degenerate. The author, whose view is 

 pretty well limited to vertebrates, tabulates 

 some 33 cases of similar acceleration of physio- 

 logically important organs and retardation of 

 physiologically degenerating organs. 



This principle of ontogenesis, while not en- 

 tirely original with the author, is elaborated by 

 him more than it has been heretofore, and 

 especial attention is directed to the fact that 

 the action of this principle nullifies many infer- 

 ences concerning ancestral conditions drawn 

 from the time of appearing, or the relative size 

 at a given age, of particular organs. Thus it 

 has been argued from the fact that children at 

 birth have proportionately larger brains than 

 adults that the relative size of the brain is 

 diminishing in the human race. According to 

 Mehnert's principle, however, the relatively 

 early attainment of a great size by the human 

 brain indicates that it is a phylogenetically pro- 

 gressing organ, which is certainly a more rea- 

 sonable as well as a more agreeable conclusion. 



Starting from this principle Mehnert now at- 

 tempts to explain phylogenesis thereby. Here 

 he takes the position of a Neo-Lamarckian in 

 respect to the inheritance of acquired characters, 

 while he accepts Weismann's general concep- 

 tion of preformation in the germ by means of 

 determinants. Individual development pro- 

 ceeds under the influence of two factors. One 

 of them consists of inherited qualities whose 

 development is the ' unfolding of phylogenetic 

 energies ;' with this has become associated the 

 second factor, the contribution of those cells 

 which have been added under the special 

 influence of the functional activity of the 

 individual ; this is the epigenetic factor. 

 The difficulty of seeing how the acquired 

 characters — the epigenetic factor — are in- 

 herited is surmounted in this way : Inherit- 

 ance is not due merely to a certain chemical 

 constitution of the germ plasm, but also to its 

 physical condition. The molecules of the germ 

 exert a formative influence over each other, 

 much as a bar magnet does over the magnetic 

 field. Now, the quality of this influence is 

 modifiable by the surrounding soma, much as a 

 piece of iron in a modern warship is afiected by 

 the distribution and varying conditions of all 

 surrounding masses of the metal. This (chiefly 

 physical) effect of soma upon germ may deter- 

 mine certain qualities in the unfolding of the 

 germ. 



And here is where the principle of organ- 

 ogenesis comes in. When an organ is much 



