274 GE0 - w - TANNREUTHER. 



BIBLIOGRAPHY. 



i. Andrews, E. A. 



'98 Ectosarcal Phenomena in the Eggs of Hydra. Johns Hopkins University Cir- 

 culars. 



2. Downing, E. R. 



'04 The Spermatogenesis of Hydra. Zool. Jahr., Band 21. 



3. Brauer, A. 



'91 Ueber die Entwicklung von Hydra. In Z. f. Wiss. Zool., 52, 2. 



4. Kleinenberg, N. 



'72 Eine anatomisch-entwicklungsgeschichtliche Untersuchung. Leipzig. 



5. Kerschner, L. 



'80 Zur Entwicklungsgeschichte von Hydra. Zool. Anz. , 3 Tahrg., Nr. 64. 



6. Korotneff, A. 



'83 Zur Kentniss der Erabryologie der Hydra. Z. Wis. Zool., Bd. 38. 





Explanation of Plate VIII. 



Fig. 1. Egg with polar bodies, immediately after it has passed to the exterior of 

 the ectoderm, e.m., egg membrane. 



Fig. 2. Section showing early formation of ovary at the time the interstitial cells 

 become differentiated into two distinct regions ; a, b, and c, cells of the central 

 region that are directly concerned in the formation of the ovum or ova ; p.r, cells of 

 the peripheral region which contribute to the formation of the yolk. X 7°- 



Fig. 3. Section, little later than preceding, showing the ovum between the inter- 

 stitial cells, which later become the yolk, and the mesoglea ; a, nucleus, which 

 becomes the egg nucleus ; b.c, nuclei breaking down within the egg cytoplasm ; m, 

 mesoglea. 



Fig. 4. Section of ovum showing the formation of the pseudopodia ; a, egg 

 nucleus ; p.s, pseudopodia. X §°- 



Fig. 5- Cross-section of ovary, little later than preceding, just before the formation 

 of the yolk or pseudo-cells. 



Fig. 6. Cross-section of several pseudopodia showing the entrance of nuclei of 

 the interstitial cells of ovary, which become the yolk. 



Fig. 7> a-e, five stages in the transformation of interstitial nuclei into yolk. 



