396 CALKINS. 



3. A higher type is shown by the "intermediate" nuclei, 

 where the chromatin granules are massed together in a compact 

 form with or without a nuclear membrane (most Euflagellates). 



4. Typical nuclei of the metazoan type are uncommon among 

 the Protozoa, but are occasionally found. 



5. Nuclear differentiation in Protozoa is closely connected 

 with an attraction-sphere or active agent in division. In nuclei 

 of the distributed type this is an indefinite faintly staining cyto- 

 plasmic mass in the vicinity of which the scattered chromatin 

 granules collect previous to division and about which they are 

 grouped during division. In nuclei of the "intermediate" type 

 the attraction -sphere is intra-nuclear, definite in form, deeply 

 staining and active, and chromatin granules are massed about 

 it either permanently [Synura, Chilomonas, Eiiglcnoids^ etc.) or 

 only during division {Paraniceba), and with or without a nuclear 

 membrane. In higher types of nuclei the attraction -sphere is no 

 longer intra-nuclear, but this position of vantage is taken by the 

 central spindle during division (^Noctiluca and many Metazoa). 



6. The intra-nuclear body oi Euglena and other allied forms is 

 equivalent to the attraction-sphere and not to the centrosome of 

 the metazoa. 



7. Chromosome-formation is first seen in the flagellates in 

 the form of rods which arise by the union of the previously scat- 

 tered chromatin granules. They form in typical though primi- 

 tive metazoan manner in Noctiluca and Englypha and all Metazoa 

 pass through these stages in preparing for mitosis. 



Columbia University, April, 1898. 



