THE EFFECTS OF BLOOD PROTEIN DEPLETION ON THE GROWTH OF THE OOCYTES IN THE CECROPIA MOTH

¹ Zoological Laboratory, University of Pennsylvania, Philadelphia 4, Penna

1. The earliest oocyte to differentiate in an ovariole of the Cecropia moth grows during the final week of its development with a daily increment in volume which was calculated to be 91% per day. Growth during this period is due primarily to the accretion of yolk spheres. It terminates abruptly when the chorion appears at the surface of the oocyte.

2. Successive oocytes in an ovariole lag behind each other in their development by an average of approximately 5 hours; the first oocyte terminates growth more than 6 days earlier than the thirtieth oocyte. As a consequence, the first oocyte produces yolk at a time when at least two prospective yolk proteins are present in the blood at higher levels than those prevailing during the growth of the later oocyte.

3. Correlated with a decline in the level of the two blood proteins are reductions in the growth rates of successive oocytes in the ovariole and in the final size which they attain. Experimental results suggest that depletion of the female protein in the blood may be one of the primary causes of the reduced vigor with which the later oocytes grow.

4. The final concentrations of the two proteins were the same in successive oocytes in the ovariole. Thus, while the normally occurring depletion in the blood's supply of prospective yolk proteins may lead to a reduction in the rate and amount of yolk formation in an oocyte, it does not affect grossly the quality of the yolk produced.

5. From a consideration of the oocyte growth curve and of cytological observations reported for other yolk oocytes, it is proposed that yolk is formed in the Cecropia oocyte by an exponentially increasing mechanism which is probably located at the periphery of the cell.

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