384 CALKINS. 



The Intermediate Tvpe of Nucleus. 



The ''intermediate type" includes those nuclei which have 

 either a faint nuclear membrane or none at all, and which per- 

 sist in the form of spherical aggregates of chromatin granules 

 about a central attractive body. The majority of the common 

 autoflagellates possess nuclei of this type and a description of 

 a few will suffice for all. The forms selected are Microglciia, 

 Syniira^ Chilojjiouas, Trachclomojias and Eiigleua. 



Microgle7ia piinctifera (PI. XXXV, Fig. 6). This minute form 

 possesses two large chromatophores which occupy the greater 

 part of the cell and which obscure the finer protoplasmic struc- 

 ture. There is a single flagellum attached at the end where the 

 chromatophores come together. At this end also a small pig- 

 mented *' eye-spot" can be made out (Fig. 6, e). The nucleus 

 lies between the chromatophores in the center of the cell. It 

 consists of a large number of chromatin granules surrounding a 

 deeply-staining central body. The granules are loosely ar- 

 ranged, often forming an irregular outline and apparently are 

 not bounded by a nuclear membrane. 



Synura tivclia (PI. XXXV, Fig. 7). This beautiful colony- 

 form is similar to Microglcna in regard to nuclear structure, and, 

 ■being larger, the details can be more readily made out. The 

 monads are attached at a central point by their sharp ends, 

 which form the lower extremity of the gelatinous mantle sur- 

 rounding the protoplasmic body. The two equal-sized flagella 

 arise from the outer end of the protoplasmic body and run nearly 

 parallel through the outer mantle. Two large chromatophores 

 occupy the greater part of the cell, each being curved like the 

 half of an empty nut shell. The nucleus is enclosed in the 

 space between the chromatophores. It is excentric in position, 

 lying nearer the flagella end. Like the nucleus of Microglcna 

 it is made up of fine granules of chromatin disposed around a 

 distinct central body. Here also the chromatin appears to be 

 free from a bounding membrane, but in both of these forms the 

 nuclei are distinctly outlined and well marked off from the sur- 

 rounding cytoplasm while they invariably appear round in 

 section. 



