248 Robert Wilhelm Ilegner. 



tionskcrn" was present. In these eggs "entstehen die Genitaldriisen 

 aus Mesodennzellen, die in die Mesodermrohren von der Banchseite 

 hereindringen." 



5. Orthoptera. 



Many papers have appeared contributing to onr knowledge of 

 the germ-cells of the Orthoptera. Unfortunately, a large number of 

 them are based on a study of one species, Blatta germanica, which is 

 not favorable for this particular phase of embryological research. 



We owe the first account of the primitive germ-cells of the 

 Orthoptera to Ayers (1883). He found the rudiments of the germ- 

 glands in Oecantlius niveus at a late embryonic stage after revolu- 

 tion of the embryo had taken place. "They are first seen as two 

 irregular groups of amoeboid cells, belonging to the splanchnic layer 

 of the mesoderm on either side of the dorsal vessel." These groups 

 of cells were transformed into ovaries in their primitive position. 



Nusbaum (1886) considered the reproductive organs of Peri- 

 planeta orienialis of mesodermal origin. 



Heymons (1890-91) made a detailed study of the origin and 

 development of the germ-glands of Blatta germanica. He found in 

 this insect a segmental origin of the germ-cells. They w^ere identified 

 as large cells, in the second to the seventh abdominal segments, which 

 arose from the splanchnic layer of the mesoderm; new genital cells 

 were continually added. Later a migration of the germ-cells took 

 place into the coelomic cavities, and afterward between the cells of 

 the dorsal walls of the coelomic sacs. Here a continuous strand of 

 germ-cells was formed on either side of the body ; these were situated 

 in the dorsal wall of the primitive somites extending from the second 

 into the eighth abdominal segment. Undifferentiated mesoderm cells 

 were added to these strands from the dorsal wall of the coelomic sacs, 

 to form the epithelium of the germ-glands. The strands now short- 

 ened, and, by the lateral pushing of the germ-band around the yolk, 

 were carried to the dorsal side of the egg where they continued their 

 growth. 



Heymons (1890) claimed to have discovered an hermaphroditic 

 condition in the male genital organs of Blatta {Phyllodromia) . "Es 

 geht hieraus unzweifelhaft hervor, dass jencr Theil der Genitalanlage 



