Section 6 — Cytology 



have revealed asynchrony in DNA synthesis 

 between the chromosomes and chromosomoids, 

 thus enhancing the grounds for their separation. 

 Photographs of intact leucocytes at metaphase 

 show a range in number of the chromosomoids 

 from sixty to ninety. Karyotype preparations of 

 these cells confirm previous observations that the 

 chromosomoids are acentric, variably hetero- 

 chromatic, morphologically inconstant and as 

 such do not fulfil any definition of a chromo- 

 some. These observations together with their DNA 

 asynchrony indicate that they constitute an 

 extension to the spectrum of known chromatic 

 entities in the nucleus. Their genetic properties 

 can only be surmised at present. 

 Full details will be published in the Int. Rev. Cyt. 



6.10. Cytophotometric Studies on the Spermatogonia 

 of Nepa cinerea (Hemiptera). Olli Halkka 

 (Helsinki, Finland). 



In the water scorpion, Nepa cinerea, the gonio- 

 mitotic divisions proceed strictly synchronously 

 in each cyst. The cyst is the smallest nutritional 

 unit of the testis. At the 8-cell stage, the mean 

 nuclear volume is about 430 |i 3 but only about 

 130 u 3 at the 128-cell (last gonial) stage. The 

 corresponding cellular volumes are about 1070 

 u 3 and 340 ia 3 , respectively. At the 8-cell stage, 

 each cell has about 250 u 3 of cyst surface area for 

 its metabolism to use while at the 128-cell stage 

 this area has decreased to about 45 n 3 . The 

 nutritional conditions of cells in a 8-cell cyst may 

 be quite different from those of cells in a cyst 

 approaching meiosis. 



The concentrations of the main chemical com- 

 ponents of the cell were determined photometric- 

 ally at different stages of testis development. The 

 amount of DNA (Feulgen dye — DNAcomplex) 

 was found to be the same in 8-cell (x = 10.35 

 arbitrary units at metaphase measured with the 

 two-wavelength method) and 64-cell (x = 9.87) 

 cyst nuclei as well as at first maturation division 

 metaphase (x = 9.30). Thus, the smaller size of 

 the chromosomes at later gonial generations is 

 due to increased "condensation" and not to a 

 change in the degree of polyteny. 



During gonial development, no statistically 

 significant change in the concentration of arginine 

 (the McLeish modification of the Sakaguchi 

 test) in the cytoplasm was found. The same is true 

 of the tyrosine and tryptophane containing 

 proteins (Millon reaction). The ratio DNA/ 

 cytoplasmic protein therefore was higher at the 

 64-cell stage than at the 8-cell stage. Highest 

 interphase concentrations of RNA (Azure B) 

 were observed at the 8-stage. 



6.11. The Formation of Chromosomal Axis in 

 Mitosis and the Function of Nucleolus. Gon- 



pachiro Yasuzumi (Kashihara, Japan). 



The present communication is concerned with 

 electron microscope studies on prophase chromo- 

 somes of Ehrlich ascites tumour cells and Pelo- 

 myxa carolinensis, and on nucleoli of sper- 

 matogonia and spermatocytes of Ascaris megalo- 

 cephala. Ehrlich ascites tumour cells, amoebae, 

 and testes of ascaris were fixed in formalin, potas- 

 sium permanganate or osmium tetroxide, buffered 

 to pH 7.4-7.8 with Michaelis veronal-acetate 

 buffer. After fixation, they were dehydrated with 

 increasing concentrations of ethyl alcohol, and 

 embedded in Epon epoxy resin or a mixture of 

 methyl- and n-butyl methacrylates. Sections 

 were cut with the Porter-Blum microtome 

 equipped with a glass knife. DNase, RNase and 

 trypsin were used singly and in combination to 

 treat formalin-fixed material in block or in 

 section. The sections were stained with a 

 slightly modified method of Watson's lead 

 acetate or uranyl acetate. They were examined 

 with an electron microscope of the Japan 

 Electron Company, model JEM-6C, or the 

 Akashi electron microscope, model TRS, 50E i. 



The mitotic early prophase chromosome deve- 

 lops from the nucleolus towards the nuclear enve- 

 lope and finally comes to a close association with 

 the nuclear envelope. An axis has been found in 

 the early prophase chromosome, consisting of a 

 pair of tubular elements. In more advanced stages 

 of prophase the axis is provided with symmetri- 

 cally disposed processes. In the nuclei of sperma- 

 togonia and spermatacytes in Ascaris nwgalo- 

 cephala at least two nucleoli are found, one of 

 which is composed of numerous dense granules 

 of varying size an shape, each granule consisting 

 of an aggregation of dense particles 110 to 150 

 A in size, but the other is almost compact. The 

 dense granules are gradually separated to the 

 composed particles which eventually appear 

 through the pores of nuclear envelope into the 

 cytoplasm. Thus the nucleolus seems to have 

 two functions: the reorganization of chromo- 

 somes in mitosis and the formation or storage 

 organ of ribonucleoprotein. 



6.12. Effect of Mono- and Divalent Ions on the 

 Structure of Isolated Metaphase Chromosomes. 



Carolyn E. Somers (Houston, U.S.A.). 



Recently, methods have been described for 

 the mass isolation of metaphase chromosomes. 

 With the isolation of metaphase chromosomes, 



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