208 I'.VKOLIXE McGlLL, 



b) In Aiiax Junius. 



(a) The Nucleoli. 



(b) The Yolk-nuclei. 



VI. Summary. 

 VII. Literature List. 

 VIII. Explanation of Plates. 



I. Introduction. 



While studyiug- oogenesis iu two of the cirag-on-flies, Anax Junius 

 and Flaihemis lydia. it was fonnd that both forms have nucleoli of 

 very interesting- structure, especially' during- the growth period. In 

 view of the recently revived idea that the nucleolus plays a definite 

 role in the metabolism of the cell, particularly in the formation of 

 chromatin, it seemed advisable to investigate carefully the origin, 

 structure and, so far as possible, the function of the nucleoli in the 

 eggs of these insects. 



At first the intention was to work cut the complete oogenesis 

 of these forms, but as yet no material young enough to show early 

 oogonial divisions, nor old enough for maturation-stages, has been 

 obtained. All the later stages of oogenesis are exceedingly difficult 

 to investigate because of the large amount of yolk present in the 

 egg of the imago, which renders sectioning almost impossible. 



This work was done in the Zoological Laboratory of the Uni- 

 versity of Missouri under the direction of Professor (teokge Lefevre 

 to Avhom I am indebted for many valuable suggestions. 



II. Literature Review. 



Because of the very comprehensive re\'iew by Montgomery (1899) 

 of the \\'ork on the nucleolus, it seems unnecessary to give a complete 

 list of the literature here. I shall only refer to those papers which 

 deal most closely with the development of the nucleoli and their 

 relation to synapsis. 



1. Origin of tlie Nucleolus. 



While most observers hold to the idea that the nucleolus is of 

 nuclear " origin, some maintain that it arises from material which 

 passes from the cytoplasm into the nucleus. 



The folloAving writers consider the nucleolus to be derived from 

 the chromatin: Retzius (1881), Strasburger (1882), Leydig (1883), 



