Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/243



WHEN treating of the different parts of the ovum, in the foregoing work, it was found impossible to give a positive solution to the question as to whether the germ-vesicle was a young cell or the nucleus of the yelk-cell. Most of the facts before us were in favour of the latter view; but if this were the correct one, the yelk-cell ought to be developed around the previously existing vesicle in such manner, that it in the first instance closely encompassed the latter, and afterwards became gradually expanded. This decisive observation was wanting, and the researches communicated by R. Wagner, in his ‘Prodromus,’ rather tended to show that, in the formation of the ovum around the germinal vesicle, the membrane was not formed immediately around the vesicle, but that it inclosed at the same time a quantity of the granular mass in which the germ-vesicle lies. I was not at that time acquainted with a work of Wagner’s, which contained the facts necessary to a solution of the question, viz. his ‘Beiträge zur Geschichte der Zeugung und Entwickelung., Erster Beitrag :’ from the ‘Mathematisch-physikalischen Klasse der Königl. Baierschen Acad. der Wissenschaften in München.’ Speaking of the ovaries of insects, Wagner says, at page 45 :— “At the spot where the oviduct widens, the granular mass, which resembles the vitelline mass, becomes more plentiful; the separate germ-vesicles seem to be imbedded in it. I have so represented it in the ‘Prodromus,’ fig. 18, Lately, however, it has appeared to me, as though the germ-vesicles with their germinal spots were actually already surrounded by a chorion and a perfectly pellucid yelk.”. The accompanying illustration from Agrion virgo exhibits clearly how that which Wagner calls chorion,