feathers, on the development of the crystalline lens, on the 

 appearance of the gall bladder in the fetus, and on the 

 development of the lungs . 



His embryological observations led Gros to certain con- 

 clusions about spontaneous development, published in an 

 article of 1847.58 In this report, after a history of the 

 speculative study of spontaneous development, Gros reported 

 with no hesitation the spontaneous development of the tape- 

 worm. He described in detail the conversion of vacuoles in 

 the digestive glands into worm eggs, the appearance of 

 embryonic vacuoles in the eggs, and their disappearance 

 before the beginning of division. 



Gros stated his opinions most completely in a long 

 article 0-30 pages) published in 1851.59 This work holds 

 interest also for the history of the theory of evolution. 

 His main objective was to affirm that organisms at successive 

 steps of creation are genetically connected with each other. 

 Thus: "Borders between the animal and plant kingdoms do not 

 exist; on the contrary, they cross each other." "A cell can 

 make a plant or an animal." "Conversion of types is proved by 

 observations." "A cell is capable of multiplication as a 

 plant Cfilaroent) or as a pseudo-animal cell (euglena) ; its 

 daughter cells could multiply later as plant or as animal 

 cells." "The cell developing as a plant provides the 

 beginning of more complex plant types" — however, some of those 

 cells, in Gros 1 opinion, constantly produce their specific 

 type, and others go in the direction of regressive evolution 

 (p. 458). "Filaments are capable of dividing into vacuoles, 

 which can be turned into animal cells and converted into a 

 number of transitional forms." "Euglena cells are related to 

 both kingdoms and, apparently, form a cross between them" 

 (p. 549). "Euglena cells demonstrate in a very clear form 

 the relationship of the two kingdoms and form the beginning 

 of two branches, one of which forms an ascending plant line, 



58. Gros, "De la generation spontanee ou primitive en generale 

 et en particulier de Helminthes , " BULL. SOC . NAT. 

 MOSCOW, 20 U847), pp. 517 -540. 



59. Gros, "De 1 ' embryo log ie ascendante des especes, ou 

 generation primitive, equivoque et spontanee et 

 metamorphoses de certains animaux et vegetaux inferieurs, " 

 BULL. SOC. NAT. MOSCOW, 24 (1851), pp. 283 - 340, 

 429 - 502. 



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