EEVIEW. 



Researches on the Composition and the Significance of the 

 Egg, based on the Study of its Mode of Formation, and of 

 the first Embryonic Phenomena — {Mammifers, Birds, 

 Crustacea, Worms). By Edouaud van Beneden^ 

 Doctor of Natural Sciences. Presented August 1, 1868; 

 crowned by the Royal Academy of Belgium in public 

 assembly December 16^ 1868. Brussels^ 1870. 



The very valuable Memoir of Dr. Van Beneden is at 

 length published, consisting of nearly 280 pages quarto, and 

 twelve excellent plates. It is impossible for us here to give 

 an adequate sketch of so extensive and valuable a Avork. The 

 numerous details and observations which it contains are, 

 however, all directed to establish certain conclusions con- 

 cerning the signification of the egg, and the various parts 

 Avhich compose it, which we shall state, referring the reader 

 with great confidence to the clear, logical, and interesting 

 details of observation given in the Memoir. " It was not," 

 remarks Dr. Van Beneden, " until after the appearance of the 

 memorable works of Von Baer, Purkinje, R. AVagner, Coste, 

 Prevost, Dumas, and Rusconi on the Vertebrata, of Rathke, 

 Herold, von Siebold, and P. J. Van Beneden on the lower 

 animals, that the bases of comparative ovology and em- 

 bryogcny were definitely established. The constitution of 

 the egg of the superior animals, and of a certain number of 

 inferior animals, was known, and it was perceived that 

 throughout the egg consists of the same essential parts : of a 

 membrane, of a vitellus, and of a germinal vesicle, holding 

 in suspension one or several refringent corpuscles. On the 

 other hand, the breaking up or cleavage which Prevost and 

 Dumas had established in the Batrachia came to be discovered 

 in Fishes by Rusconi and Von Baer ; Von Siebold pointed it 

 out in certain Nematods ; Duniortier, Van Beneden, and 

 A¥indischman in some Gasteropods. 



But what a mystery this segmentation was — manifesting 

 itself everywhere Avith the same characters ! What relation 

 could it have to the formation of the embryo, and what could 

 be its object? This was, indeed, an enigma which seemed 

 to be impenetrable, and one knew no more Avhy the vitellus 

 divided itself up into bits, than one could guess why the egg 



