230 W. M. SMALLWOOD. 



SUMMARY. 



1. In many particulars this work is a confirmation of the pre- 

 vious paper by Hargitt, especially in regard to the several nuclei 

 in the unsegmented egg, the irregular shape of many such nuclei, 

 and the irregular phases of cleavage. 



2. The ova arise in any region of the polyp, which is contrary 

 to Bunting's statements. The young ova gradually increase in 

 size, during which time the nucleolus becomes vacuolated and the 

 cytoplasm is occupied by numerous microsomes which become 

 transformed into spherules. The cytoplasm changes its staining 

 reaction during this time. 



3. The chromatin during the growth of the egg stains less in- 

 tensely than when in the younger state. Much of the chromatin 

 migrates into the cytoplasm and is surrounded by vacuoles. 

 The highly vacuolated condition of the cytoplasm is probably 

 directly due to this migrating chromatin. The size of the nucleus 

 decreases greatly. 



4. In Hydractinia there were found three distinct kinds of 

 granules, yolk masses, coarse granules and small bodies around 

 the periphery. The small granules are distributee exclusively to 

 the ectoderms. 



5. Maturation begins in Hydractinia before the eggs are de- 

 posited. The process is by the formation of a distinct mitotic 

 figure. It is very rare to find a polar body attached to the 

 deposited egg. 



6. The female pro-nucleus is very much smaller than the egg 

 nucleus before maturation but it persists as a definite structure 

 until cleavage begins. It is not at any time indistinguishable. The 

 male pro-nucleus moves through the cytoplasm until it approaches 

 the female pro-nucleus when the two fuse and fertilization is 

 effected. 



7. The first, and all subsequent cleavages, is by the mitotic 

 process. A definite segmentation cavity is formed in the two- 

 celled stage which increases in size. This cavity is gradually 

 filled with cells until the planula is a solid mass of cells. 



8. The false membrane in Pennaria is a transitory structure 

 and probably of a fluid nature. Later its place is taken by a true 

 membrane. 



