NUCLEI AND KINETIC ELEMENTS 



65 



similar size and are densely packed throughout the entire nucleus, 

 giving a characteristic appearance after staining. They are widely 

 distributed in Dinoflagellata, Ciliata and Suctoria, but there is con- 

 siderable variation in their density in different species, especially 

 in the Infusoria. In some of the micronuclei {e. g., Paramecium 

 caudaUim, Euplotes patella, etc.), the chromidiosomes are so tightly 

 packed as to give them, more than any other type of protozoon 

 nucleus, the aspect of a spermatozoon head (Fig. 22, Z), E, F). In 

 other cases the granules are very fine and follow the course of the 

 linin network thus affording an excellent picture of the alveolar 

 structure within the nucleus. 



Fig. 27. — Chromidia formation in Mastigella and Mastioina. A, B, young forms 

 of Mastigella vitrea prior to chromidia formation ; C, chromidia arising from the nucleus 

 D, young form of Mastigina setosa with accumulation of chromidia; E, F, mature 

 stages of M. setosa; G, formation of gametic nuclei (a) from scattered chromidia. 

 (After Goldschmidt.) 



The formation of the massive tApe of nucleus during reorganiza- 

 tion after conjugation is clearly shown in the case of Uroleptus 

 mobilis (Fig. 1, Frontispiece). The young macronucleus is formed by 

 a second division of a fertilization nucleus after conjugation when it 

 appears as a vesicular nucleus with a fine linin reticulum which has 

 no staining capacity. In life it appears like a large, highly refractile, 

 vacuole. It remains in this ghost-like condition for a period of three 

 or four days, enlarging meanwhile and becoming ellipsoidal in form. 

 Chromatin ultimately makes its appearance in the form of minute 

 granules on the nuclear reticulum. These granules increase in 

 number and in size until the characteristic dense nucleus with 

 intense staining capacity results (Fig. 2S). It then divides with the 



