244 Robert Willielm Hegner. 



to^ 



whole mass divided into horseshoe shaped halves which migrated to 

 either side of the body. No "Genitalhiigel" was found in Aspidiotus 

 nerii, Corixa and Psylla. In the larva of Psylla, however, Metsch- 

 nikoff described the germ-glands as follows : "Dicht neben den Lappen 

 des secundiiren Dotters beiinden sich jederseits bei den Larven und 

 Imagines von Psylla, die Geschlechtsorgane — ein Umstand, welcher 

 fiir meine Meinung iiber die Rolle des secundiiren Dotters als Fort- 

 pflanzungsmaterial zu sprechen scheint." 



The development of both the parthenogenetic and the fertilized 

 eggs of the Aphids was studied by Balbiani (18GG-1872). In the eggs 

 of the viviparous Aphids this author (1866) was able to see "un 

 noyau granuleux fort pale dans la vesicule posterieure, moins nette- 

 ment dans I'anterieuro, celle-ci presentent done tons les caracteres 

 de veritables cellules. Ce sont ces vesicules ou ces cellules qui vont 

 etre I'origine des elements gencrateurs males et femelles du futur 

 animal, . . ." In the developing winter egg the first germ-cells 

 were found by Balbiani (1869-1872) at a later stage. They formed 

 an oval structure which lay in the median line of the body and soon 

 divided lengthwise into halves. 



Witlaczil (1884), in viviparous x\phids, also recorded a single 

 primitive germ-cell which separated from the inner surface of the 

 blastoderm at the posterior end of the egg. This single cell grew 

 rapidly, producing by division a group of round clear cells each 

 containing a large nucleus. This mass of cells was attached to the 

 tail-fold, and moved with this until it reached a position in the 

 posterior dorsal region of the body. During the revolution of the 

 embryo, the rudiment of the germ-glands divided, half going to 

 either side of the alxlomen. 



The origin of the germ-cells of viviparous Aphids was investigated 

 by Will (1888). This author found that a thickening took place 

 in the lateral wall of the blastoderm. "Bald aber sieht man die 

 obersten Zellen der verdickten Cylinderseite sich in besonderer Weise 

 differenziren ; sie wachsen sehr schnell zu ansehnlicher Grosse heran, 

 nchmen polyedrische Gestalt an und zeichnen sich durch eine ge- 

 ringere Tinctionsfahigkeit ihres Plasmaleibes sowie eine andre Be- 

 schaffenheit des Kernes aus. Durch rcge Theilung vermehren sie 



