THE GERM-CELLS OF CICADA (TIBICEN) SEPTEMDECIM. 435 



could pass through the membrane unless they be in a fluid, diffus- 

 ible state, and if so they would become diffused when they 

 entered the cytoplasm. Cases of "extruded nucleoli " have often 

 been mentioned in the literature, but it must be said that many 

 of the interpretations are exceedingly doubtful. In Cicada, 

 when the ovaries have been fixed for a considerable length of 

 time (24 hours) in Bouin's fluid, the mitochondria entirely dis- 

 appear, leaving occasionally traces of their dissolution in the form 

 of cytoplasmic vacuoles in the region of the nucleus (Fig. 82). 

 By fixing the ovaries in Bouin's fluid for varying lengths of time 

 (5 to 12 hours) a variety of peculiar structures may be found in 

 the cytoplasm which are all referrable to the various stages and 

 degrees of dissolution of the perinuclear zone of mitochondria 

 (Figs. 39, 41, 42, 80, 81, 82). When the ovaries are fixed for ten 

 hours in Bouin's fluid, a zone of the cytoplasm is found around 

 the nuclei of the oocytes which takes the plasma stain intensely 

 (Fig. 42). Within it may be found vacuoles and deeply staining 

 bodies resembling those structures which Vejdovskv ('12) 

 figures in Aphrophora. In studying the effect of acetic acid of 

 fixing fluids upon the mitochondria, I am led to believe that 

 many of the peculiar cytoplasmic bodies which have been de- 

 scribed and figured in germ-cells under various names such as 

 extruded nucleoli or plasmosomes, vacuoles, idiozomes, spheres, 

 yolk-spherules (Dotterkugeln), etc., are the result of imperfect 

 fixation of mitochondrial substances. O. Vander Stricht ('04) 

 has shown a similar effect of reagents in the distortion and dis- 

 solution of mitochondria in the "couche vitellogene" of the 

 oocyte of the bat. 



(b) Yolk-formation. Throughout the growth period of the 

 oocyte, the mitochondria increase greatly in numbers and con- 

 tinue to be located in the well delimited perinuclear zone. At 

 the time when the cytoplasmic volume of the oocyte is at its 

 maximum (Fig. 85) the zone of the mitochondria occupies ap- 

 proximately a third of the cytoplasmic volume. After this stage 

 in the growth of the oocyte, the perinuclear mitochondrial mass 

 begins to loose its well-defined zonal limits and the granules 

 become dispersed in the cytoplasm towards the periphery of the 

 oocyte (Fig. 86). The migration of the mitochondria from the 



