OCTOBEK 14, 1898.] 



SCIENCE. 



519 



system, wliicli can be stored up in it, and be- 

 come internal causes, manifesting themselves 

 again, in the sequence, in induced phenomena 

 within the system, for the explanation of which 

 they must be used." 



The weakest part of the whole book is the 

 chapter entitled ' Die im Organismus der Zelle 

 enthaltenen Factoren des Entwicklungspro- 

 cesses.' For the author, all these factors are 

 included in the nucleus ; the protoplasm is iso- 

 tropic ; variation in the size and in the rate of 

 cleavage of the cells are due entirely to the 

 distribution of yolk ; and its distribution to 

 gravity. "The accumulation of yolk in the 

 «gg-cell undoubtedly exercises a far-reaching 

 influence on the course of development, im- 

 pressing on it a special character. On this ac- 

 count many investigators have been induced to 

 regard the egg as something more than a simple 

 cell," etc. (italics mine). "But the character 

 of the egg as a simple cell is not in the least 

 altered by the accumulation of material in it." 

 Whitman is supposed to hold this idea, that the 

 degree of organization of the egg is proportional 

 to the amount of yolk in it. Such a grotesque 

 conception of Dr. Whitman's views is inex- 

 cusable. To say that "the inequalities which 

 arise in the size and the arrangement of the 

 embryonic cells and in their yolk-contents have 

 nothing to do with the differentiation of or- 

 gans ' ' is simply untrue, as is . proved by the 

 whole subject of cell-lineage, which has put the 

 problem here discussed in an entirely new light, 

 about which a voluminous literature has already 

 arisen, but which is not even mentioned by 

 Hertwig. Think of such a phrase as this : ' the 

 organization of the egg, which depends on the 

 inclusion of deutoplasm !' (p. 265). 



The third foundation-stone of the theory of 

 Biogenesis is the principle of progression. A 

 single quotation will suffice to indicate what is 

 meant by this: "Placing ourselves upon the 

 theory of descent, might we not suppose that 

 species develop according to the principle of a 

 steady progression regulated by law, like the 

 multicellular organism by epigenesis from the 

 egg, not as the sport of circumstances, but with 

 the same innate necessity that causes the gas- 

 trula to succeed the blastula in ontogenesis?" 

 The principal points of view of the theory of 



Biogenesis are summarized by Hertwig in the 

 concluding pages ; they may be condensed 

 thus : 



1. "Since all organisms pass through the 

 unicellular conditions in their development, all 

 constant or essential characters by which species 

 is distinguished from species must be contained 

 in their simplest form, or, so to speak, reduced 

 to their simplest expression in this. There are 

 thus as many fundamentally different species of 

 cells as there are different species of plants and 

 animals." 



2. The essential distinctions between these 

 cells are not directly discernible. But from 

 logical considerations we are forced to assume 

 "that the cells possess a finer micellar organi- 

 zation exceeding our powers of observation, by 

 virtue of which they are the bearers of the 

 properties of the species," and that this sub- 

 stance, the idioplasm, makes up only a small 

 part of the whole substance of the cell. ' ' Ac- 

 cording to our theory it is contained in the 

 nucleus." 



3. "The cause of continuity in development 

 is that each individual is the product of a cell 

 possessing the same specific properties." 



4. As to the causes of the development of the 

 individual from the species-cell, the theory of 

 Biogenesis postulates ' the increase of the 

 species-cell and the correlative process of social 

 union, division of labor and integration.' 



5. The process of cleavage is a multiplication 

 of the original cell, all products possessing the 

 same fundamental organization. 



6. "The aggregate takes on definite forms 

 during its growth, which in any stage are the 

 expression of: (1) the influence of innumerable 

 external factors ; but still more (2) of the end- 

 lessly complicated effects which the constantly 

 increasing elementary units exercise on one 

 another." 



7. ' ' Within the series of generations of per- 

 sons, or between the separate ontogenies, the 

 continuity of development is preserved by single 

 cells freeing themselves from the aggregate of 

 the species-cells and becoming the origin of a 

 new process of development." 



In conclusion ,1 cannot avoid criticising the 

 name which the author has chosen for his 

 theory of development. It is not in anj' sense 



