212 Caroline McGir.L, 



can be obtained in abundance at all seasons of the year, in winter 

 by dredging the bottom where they lie buried in the mud, and in 

 summer by dipping them np in a hand-net as they are swimming 

 about in the water. 



Fresh as well as preserved material was used. In fact, these 

 forms are very favorable indeed for the study of the living egg- 

 cell, and almost all the details of the structure that can be made 

 out in the fixed and stained egg-strings can be as clearly demon- 

 strated when the ovaries are examined in fresh salt-solution. As the 

 egg-strings are closely crowded together in the ovary, they show 

 best when teased apart with needles before observing. By thi» 

 method the arrangement of the egg-strings in the ovary is also 

 clearly made out. Intra-vitam stains w^ere employed and serve well 

 to bring out the nucleoli. 



To examine the minute structure of the protoplasm, however^ 

 sections were indispensable, and for this a large number of the 

 ordinary fixatives and stains were used. 



For fixation, Flemming's and Gilson's fluids gave the best 

 results, although the common reagents such as alcohol, sublimate. 

 etc., served very well, as the material is not difficult to fix. 



The abdomens of the larvae were opened while submerged in 

 normal salt-solution; the ovaries were removed by clipping with fine 

 scissors, and were transferred as quickly as possible to the fixing 

 fluid. 



Of the large number of stains used the following may be men- 

 tioned as giving especially good results: Heidenhain's iron-haema- 

 toxylin, Flemmikg's triple stain and the borax-carmine, methyl-green 

 method of Obst (1899). Stained by iron-haematoxylin the chromatin 

 or nnclein is black during mitosis, various shades of gray w^hen the 

 nucleus is in the resting condition. The true nucleoli, or para- 

 nucleins, in most cases are lighter than chromatin during mitosis 

 and darker in the resting cell. Flemming's triple stain colors resting 

 chromatin purplish-red; true nucleoli and chromatin during mitosis 

 violet. The method of Obst stains chromatin and cytoplasm red; 

 true nucleoli dark blue. Very often there is a blending of the two 

 differential stains in the chromatin and also in the nucleoli, indi- 

 cating that probably in the metabolism of the cell there are transi- 

 tions from nuclein to para-nuclein, and vice versa. This will be 

 I'eferred to later. 



Longitudinal and transverse sections of varying thicknesses 



