140 Harry Lewis Wieman. 



dorsal wall of the mesoblastic somites. Later, Heymons ('95), 

 extended his work to the Dermaptera and Orthoptera, and confirmed 

 this conclusion. Wheeler ('93) in Xiphidiurn ensifermis was 

 unable to detect the germ cells until the somites are formed when 

 they appear as metameric cell clusters, each of which is confined 

 to the median portion of the splanchnic w^all of the somite. These 

 two authors do not agree as to the exact time of appearance of 

 the primordial germ cells, but they show very clearly that certain 

 cells, differing from the ordinary mesodermal or epithelial cells 

 are established at an early period in ontogeny, and constitute the 

 material from which the germ cells arise. Carriere und Burger 

 ('98), came to similar conclusions for Chalicodoma muraria. 



In a study of the embryology of Donacia crassipes, Hirschler 

 ('09) states, ''die Geschlechtsanlage bei Donacia schon vor der 

 Entwicklung desselben an der ganzen Eioberflasche als histo- 

 logisch differenzierte Zellenanhaufungen auftritt. Die Genitalzel- 

 len sind also ontogenetisch alter als die Keimbatter" (p. 637). 

 More recently, Hegner ('09), published the first connected 

 account of the Keimbahn in insects, which established beyond a 

 doubt the early differentiation of the germ cells, thus exclud- 

 ing the possibility of the presence in the egg-tube of indifferent 

 cells which might give rise to either epithelial or sexual cells. 



Between these early embryonic stages and the adult condition, 

 there is a wide gap in our knowledge of the developmental process. 

 Fairly extensive comparative studies based on adult and slightly 

 younger stages have been made (Gross ('03), Kohler ('07) etc.), 

 but in order to study the history of a continuous developmental 

 process such as the differentiation of the elements of the ovary, it 

 is necessary to have a complete series of normal stages taken from 

 a single type. One can not tell from an examination, however 

 intensive, of the completed adult structure, how that structure has 

 been brought about. Inspection of a large number of sections 

 taken from later developmental stages, especially larval and pupal, 

 indicated to me that a study of this period of the formation of the 

 ovary would yield interesting and important data, and throw 

 some light on the histology of the adult organ. 



The adult female reproductive organs of L. Signaticollis con- 



