GERMINAL VESICLE AND FIRST EMBRYONIC NUCLEUS. 159 



on the germinal vesicle in an echinoderm of our coasts, 

 Asteracanthion rubens. The result of my researches is that, 

 in this animal, Wagner's spot disappears in the germinal 

 vesicle before the characters of the latter are altered. It 

 cannot be supposed that in the starfish Wagner's spot under- 

 goes progressive modifications which bring about its com- 

 plete dissolution in the germinal vesicle, and that this element 

 becomes in Toxopneustes lividiis one of the first constituent 

 parts of the first cleavage nucleus. If M. Hertwig has not 

 seen the germinal spot undergo any modifications, we need 

 not conclude, I think, that such modifications do not occur. 

 His own figures, indeed, will I think show that in Toxo- 

 pneustes Wagner's spot undergoes the same modifications as 

 in the starfish. 



Before relating my observations on the disappearance of 

 the germinal vesicle in Asteracanthion ruhens, I must state 

 shortly in what circumstances, for what reasons, and with 

 what ideas I undertook these researches. When I presented 

 to the Academy my memoir on the composition and signifi- 

 cance of the egg, I was convinced that the germinal vesicle 

 does not disappear, but that it divides, after fecundation, so 

 as to produce the nuclei of the two first cleavage-spheres.' 



Up to the time when Johann Miiller published his 

 researches on Entoconcha mirahilis'^ no one had any doubts 

 as to the disappearance of the germinal vesicle. Leuckart, 

 in his article '^Zeugung," published in Wagner's Hand- 

 worterbuch, expressed as follows the conclusion which he 

 felt authorised to draw from a comparison of all the re- 

 searches made on this subject.^ 



" Fassen wir alle diese Thatsachen zusammen, dann kann 

 es wirklich kaum noch zweifelhaft bleiben dass das Ver- 

 schwinden des Keimblaschens einen Vorgang bezeichnet, 

 der mehr der Bildungsgeschichte des Eies, als der En- 

 twickelungsgeschichte des spateren Embryo zugehort. Das 

 Einzige, was der Aufbau eines neuen Thieres voraussetzt, 

 ist die Anwesenheit eines entwickelungsfahigen Materiales." 



"If we put all these facts together, there can indeed hardly 

 remain any doubt that the disappearance of the germinal 

 vesicle indicates a process belonging more to the history of 

 the formation of the egg than to the later history of develop- 



) " Recberches sur la Composition et la Signification de I'ceuf basees sur 

 I'Etude de son mode de Formation et des Premiers Pbenomenes Embryon- 

 naires," ' Mem. Couronne de I'Acad. Hoy. de Belgique,' T. xxxiv. 



2 Job. Miiller, " Ueber Synapta Digitata und iiber die Erzeugnng von 

 Schnecken in Holotbiirien," Berlin, 1852, p. 17. 



* " Handwoi-terbucii der Pbysiologie von R. Waener," 'Art. Zeugung 

 von R. Leuckart,' p. 922. 



