R. C. VON BORSTEL 



179 



nucleic acid from the nurse cells has broken down into units 

 soluble in hot acid. This implies that it is in the form of mono- 

 nucleotides or oligonucleotides of low order. Since most of the 

 deoxyribonucleic acid is probably in small units, this could ac- 

 count for failure to find transformation, which would be a pre- 

 dictable consequence of incorporation of large blocks of deoxyri- 

 bonucleic acid from nurse cells. Also, except under unusual 

 circumstances, nuclear mutation reflected in the phenotype can 

 be only of an order that is not reparable by cytoplasmic deoxyri- 

 bonucleic acid. After nurse cell incorporation, the mature egg 



FUSION NUCLEUS AND PRONUCLEUS 



CLEAVAGE X 



PERIPHERAL MIGRATION 



YOLK PHAGOCYTE FORMATION 



Fig. 5. Diagrammatic representation of nuclear activities during meiosis, 

 nuclear cleavage, and peripheral migration in the Habrohracon egg. 



now resides in the uterine sac, and the oocyte nucleus proceeds 

 through diakinesis and metaphase. Meiosis is blocked at late 

 metaphase or early anaphase of the first meiotic division, and the 

 egg is ready to be oviposited. 



The egg is 600 microns long and 150 microns across at its 

 widest place. It is concave-convex in shape and the anterior end 

 of the embryo is the widest. The egg is positioned at least par- 

 tially in accordance with the orientation law of Hallez (1886), 

 that is, with the anterior end of the future embryo pointing to- 

 ward the anterior end of the mother while residing in the uterine 



