422 
PROF. B. T. LOWNE ON THE STRUCTURE AND 
must last several weeks. A ripe egg is first found in tlie lowest 
part of the ovarian follicle after tire 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 different stages of forma- 
tion.” 
“ The development of these eggs takes place as follows. The 
large cells which lie within 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 appears 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 yon einer einzigen Zelle abstammt, sondern 
ein ebenso zusammengesetztes Grebilde ist als die Eier der Cestoden und Trema- 
toden, bei denen Dotterstock und Keimstock ikre Producte zur Bildung des Eies 
zusainmenfliessen lassen ” (/. c. p. 209). 
t “ Es ist ruir nun gelungen, an einer Reike yon Insekteneiern sicker einen 
Austritt yon grossen Ballon aus dem Keimblascken zu constatiren, die sick 
