DEVELOPMENT OF THE OVAETES IN THE BLOWFLY. 



423 



Such an outstreaming of nuclear particles (Ballen) is un- 

 doubtedly seen in the lowest nucleus of the egg, but it also 

 occurs in the nuclei of the so-called nutrient cells, and in all the 

 nuclei of the various organs of the larva during their degeneration 

 in the first stages of the pupa. It is one of the most charac- 

 teristic phenomena of yelk-formation, whether in the egg or the 

 pupa, whilst it is quite unlike anything which has been observed 

 in relation to the well-known germinal vesicles of other animals. 



Lastly, Henking (9) has quite recently figured and described 

 the ripe ovarian egg of the Blowfly with the nutrient cells 

 outside the chorion, and his figure has fortunately enabled me 

 to discover the error into which Brandt and his followers have 

 fallen. The appearance represented by Henking is an excep- 

 tional phenomenon which I have frequently observed. When 

 the eggs approach maturity they enlarge so rapidly that the 

 anterior pole of an egg is often pushed into a chamber above 

 it containing a half-developed ovum, which then assumes the 

 form of a cap over the anterior pole of the ripe egg. I 

 have sections which exhibit this phenomenon in several stages. 

 "Whenever the young ovum in the chamber above the ripe egg 

 is present in an un-deformed condition the cap on the ripe 

 egg is absent, and whenever a cap is present there is no second 

 chamber in the egg-follicle. So many of the egg-tubes exhibit 

 transitional conditions in which the ripe egg impinges upon or 

 slightly indents the half-formed egg in the chamber above it that, 

 with good sections, I cannot believe anyone would have the 

 slightest doubt as to the nature of the phenomenon. 



2. The Development of the Ovaries mid Ova. 



The earliest stage of development in which I have as yet seen 

 the ovaries of the i^'ly is in the four-day old pupa (PI. XXYIII. 

 fig. 4). In this stage they are apparently slightly in advance of the 

 stage described by Weismann as that of the seven-day-old pupa. 

 The discrepancy is probably due to the fact that I worked in 

 summer, and Weismann's observations were made in winter. The 

 earlier stages of the pupa are well known to be greatly influenced 

 by the external temperature. 



nachher im Eiplasma auflosen. Spater verschwindet das Keimblaschen von un- 

 seren Blicken, bis wir endlich am obereu Eipol den Furchungskern wieder- 

 finden" {I. c. p. 12). 



