Nutrition of the Ovum of Scolia Dubia. 135 



Throughout the extent of the terminal chamber ova are distributed. 

 Except for the one or two at the distal end of the terminal chamber, 

 which are surrounded by apparent degeneration products, all the 

 ova show extremely short yolk ducts which connect them with certain 

 of their attending nurse cells. These yolk ducts have a wall, which 

 appears as a ring formed by the blending or coalescing of a region 

 of the cell membranes of nurse and egg cells, and a central core of 

 cytoplasm. The wall when seen in profile is extremely short, measur- 

 ing in the youngest stages .25 micron and at its maximum size 1 

 micron (Figs. 2 to 5). When seen in transverse section it appears 

 as a ring with a comparatively wide body and a diameter of from 

 2.5 to 4 microns. The wall of the duct stains intensely with all 

 the stains employed as mentioned above. In all the preparations it 

 reveals a homogeneous structure and shows no constituent granules 

 such as Giardina, '01, describes. The cytoplasmic core is not 

 conspicuous except in the late phases of its duration when it becomes 

 greatly elongated (Fig. 5). Unlike the similar structure described 

 by Giardina for Dytiscus this core showed no affinity for particular 

 stains which would give a differential stain. 



As the ovum develops and passes proximally through the terminal 

 chamber, the ring-like yolk ducts become more prominent and their 

 core of connecting cytoplasm may be seen. The maximum develop- 

 ment is reached before the nurse follicle is formed. 



The yolk ducts appear first on all sides of the ovum. After their 

 maximum development is attained, the proximal ones separate from 

 the ovum, and the nurse cells thus freed take a position distal to the 

 ovum which they attend, and enter the cell group of the developing 

 nurse follicle. Thus with the near approach of the complete forma- 

 tion of the nurse follicle, only a few of the nurse cells — the distal 

 ones — retain their yolk ducts (Fig. 5). These few ducts are event- 

 ually severed by the crowding of all the nurse cells away from the 

 ovum into .the completed nurse follicle (Fig. 6). 



The nurse cells may be considered gland cells which secrete mate- 

 rial for the ovum. The nuclear pattern of the cells having yolk ducts 

 differs strikingly from that of the other nurse cells. These chromatin 

 differences furnish additional evidence that the yolk ducts above 

 described have to do with a nutrition phase. 



