rand: nervous system of lumbricid^e. Ill 



The chromatic substance is scattered about in the form of small 

 granules, approximately spherical in shape but more or less irregular. 

 They are often not sharply outlined and appear as if imbedded in some 

 achromatic substance. The chromatic granules are mostly collected 

 about the periphery of the nucleus where, with the achromatic sub- 

 stance, they form a very loose, irregular network. Many of the chro- 

 matic masses appear to lie directly upon the nuclear membrane. The 

 central region of the nucleus is often quite free from chromatic ma- 

 terial. The occurrence of small sharply stained chromatic granules 

 close about the nucleolus, or lying directly upon its surface, is a very 

 common condition. Figures 1, 2, and 3 show these well. 



Rather coarse strands of achromatic material form more or less of a 

 network between the chromatic masses. There is often a tendency 

 toward a radial arrangement of this network about the nucleolus, which 

 appears supported within the nucleus by thai means (Figures 3 and 4). 

 The nuclear membrane is always very sharply outlined, being empha- 

 sized at the median plane of focussing by the occurrence of chromatic 

 masses upon it. 



h. The Cytoplasm. 



Very little can be said as to the finer structure of the cell proto- 

 plasm. The most careful examination fails to reveal its precise nature. 

 It varies in degree of homogeneity somewhat according to the size of 

 the cell. In the smaller cells (Figures 4, 7, 8, and 9) it usually 

 appears compact and fairly homogeneous. In larger cells (Figures 2 

 and 3) it is much less homogeneous, and there is a tendency toward the 

 formation of large vacuolar spaces, as seen at the process end of the 

 cell in Figure 2. 



The substance of the fixed cytoplasm, as it appears to the eye, may 

 be said to be of four kinds. There is (1) a perfectly homogeneous 

 " ground," represented by the lightest areas in the figures ; (2) material 

 which gives the impression of being very finely granular ; in the smaller 

 cells this material is quite evenly distributed, while in the larger cells it 

 tends to concentrate in regions, giving the cytoplasm a blotchy appear- 

 ance ; (3) rather conspicuous granules or masses staining fairly deeply 

 and often surrounded by an area within which the material of the sec- 

 ond class is less dense, as best seen in Figures 2 and 3 ; (4) fine fibres 

 irregularly distributed throughout the cell body, but often appeai'ing to 

 be associated with the more conspicuous granules and sometimes occur- 

 ring about granules as centres of radiation, as can perhaps be recognized 



