156 



GENERAL EMBRYOLOGY 



to suppose that the all-important " organization" of the ovum 

 may in some way be related to this process of chromatin 

 distribution. 



The fact of maturation has been determined for all groups of many- 

 celled animals and plants, and among the unicellular forms it is by no 

 means uncommon. Among the Protozoa the phenomena of maturation 

 are of considerable theoretical interest. In those forms in which the 

 chromatin is not formed into definite chromosomes, but remains unor- 



FIG. 81. Maturation phenomena accompanying conjugation in the Rhizopod, 

 Actinophrys sol. From Calkins, "Protozoa," after Schaudinn. A. Parts of 

 two individuals, fused; the axial filaments terminate in granules on the surface 

 of the nucleus. B. Nuclei in prophase. C. Formation of first polar spindle. 

 D. Reconstruction of nuclei. E. Fusion of nuclei. F. First division spindle. 

 p, polar body. 



ganized, grossly, there seems to be a kind of division of labor between 

 vegetative and kinetic (reproductive) forms of chromatin. The repro- 

 ductive nuclei (idiochromidia) are frequently distinctly separate from 

 the somatic nuclei (chromidia), and just before fertilization the former 

 may divide twice in rapid succession. This process bears the greater 

 resemblance to the maturation of the ovum since after each division one 

 of the two products degenerates, often without actually being thrown 

 out of the cell, leaving functional only one of the four products of the 

 original idiochromidium. Actinosphcerium is a typical example (R. 



