422 



PROF. B. T. LOWISTE ON THE STRTJCTUEE AND 



must last several weeks. A ripe egg is first found in the lowest 

 part of the ovarian follicle after the insect has flown about for a 

 long time ; then a second, third, or even a fourth chamber has been 

 developed in which there are eggs in difierent stages of forma- 

 tion." 



" The development of these eggs takes place as follows. The 

 large cells which lie withiu the epithelium of the egg-chamber 

 enlarge, by their rapid growth they lose their original spherical 

 form and appear flattened against each other as more or less 

 hexagonal sections of a sphere." 



" These cells each enclose a very distinct transparent vesicular 

 nucleus, and consist of homogeneous, but highly refractive cell- 

 substance. With increase of the cells by growth this cell-sub- 

 stance becomes finely granular and afterwards dark and yelk-like. 

 The cell-membranes then disappear, and the yelk formed in the 

 cells fuses into a mass ; so also all the nuclei disappear except one, 

 which becomes the germinal vesicle. It aj)pears that the nucleus 

 of the cell which lies lowest in the chamber always furnishes the 

 germinal vesicle. This seems to have orginated Meyer's state- 

 ments." 



Weismann concludes with the words *, " So far as the Diptera 

 are concerned, my view accords with Lubbock's ; we agree that the 

 egg of the Diptera is not derived from a single cell, but is a com- 

 pound formation, like the egg of Cestodes or Trematodes, in which 

 a germogen and vitelligen combine their products, for the com- 

 position of an egg." 



Stuhlmann (25) holds the same views as Brandt with regard 

 to the fate of the nutrient cells, and renews the old controversy 

 with regard to the germinal vesicle. The principal results at 

 which he arrives concerning it are summed up by him in the fol- 

 lowing words : — " I have been enabled by a series of observations 

 on insects' eggs to establish the extrusion of large balls from the 

 germinal vesicle which are afterwards lost in the egg-plasm. 

 Later the germinal vesicle disappears until at last at the upper 

 egg-pole we again find it as the segmentation nucleus " f- 



* Dass das Ei der Dipteren nicht von einer einzigen Zelle abstammt, sondern 

 ein ebenso zusammengesetztes Gebilde ist als die Eier der Oestoden und Trema- 

 toden, bei denen Dotterstock und Keimstock ihre Producte zur Bildung des Eies 

 zusanamenfliessen lassen " {I. c. p. 209). 



t " Es ist mir nun gelungen, an einer Reihe von Insekteneiern sicher einen 

 Austritt von grossen Ballen aus dem Keimblasehen zu constatiren, die sich 



