1919] 



Kofoid-Sivrzjf: Triclionympha campanula 



73 



The formation of distinct chromosomes takes place in the nucleus 

 some time before any signs of division may be detected in the remain- 

 ing structures of the body (pi. 7, fig. 23). The nuclei shown in 

 figures 14 to 22, plate 6, and figures 25 and 26, plate 7, show 

 different steps in this process. The number of threads or chromo- 

 somes that result has not been made out clearly at this stage. With 



Fig. T>. Diagram illustrating the phases of nuclear mitosis in Trichunympha 

 campanula. One-half the number of chromosomes is shown. 1-7. Prophase. 1. 

 Vegetative phase of ehromatin-encrusted network. 2. Splitting of the chromo- 

 somes. 3. Separation of chromosomes resulting from splitting but paired arrange- 

 ment noticeable. 4. Paradesmose formed between daughter centroblepharoplasts. 

 5. Formation of loops ; nucleus approaching elongated paradesmose. (i. Tangled 

 stage in which pseudosynapsis occurs. 7. Number of chromosomes reduced one- 

 half. 8. Metaphase; looped chromosomes unfolding on the spindle. 9. Late 

 anaphase ; paradesmose still connecting centroblepharoplasts. Chromosome marked 

 A is splitting in figure 2, appears as two chromosomes in 3 to 5, is reunited in 7 

 and 8, and separated into two distinct chromosomes in 9. The small coiled 

 chromosome is the heterochromosome. 



their first appearance, however, signs of splits in the threads may be 

 detected (pi. 7, fig. 25; text fig. D). In the following stages these 

 threads become clearer and their number may be ascertained. The 

 nucleus is then found to contain fifty-two chromosomes arranged 

 somewhat in pairs (pi. 9, fig. 44; text fig. D), that is, the end of one 



