204 NUCLEAR TRANSPLANTATION 



taining them; for example, large nuclei and nucleoli are generally 

 indicative of rapid cytoplasmic synthesis associated with growth 

 or secretion. In addition, numerous cytochemical assays of nu- 

 clear composition show that nuclei of different tissues of the same 

 organism vary both quantitatively and qualitatively (within the 

 sensitivity range of the tests employed) in content and synthesis 

 of special enzymes, proteins, protein precursors, nucleic acids, 

 glycogen, lipoprotein, etc. (see reviews by Boivin, Vendreley, 

 and Vendreley, 1948; Mirsky and Ris, 1949; Brachet, 1950, 1952, 

 1955; Caspersson, 1950; Caspersson and Schultz, 1951; Novikoff, 

 1952; Stern et al, 1952; B. C. Moore, 1952; Pollister, 1952, 1954; 

 Fankhauser, 1954). 



In addition to evidences of chemical variation, unequal chro- 

 mosome composition has been reported in the cells of a number of 

 plants and animals. Of these, the earliest and still one of the most 

 striking examples is found in the work of Boveri and others (see 

 review by Tyler, 1955) on chromatin diminution. This occurs 

 during the early cleavage divisions of the somatic cells of Ascaris, 

 whereas the primordial germ cell retains the full chromatin com- 

 plement. Somewhat comparable differences are found in the 

 somatic and germ cells of certain insects, e.g., the fungus fly, 

 Sciara (Metz, 1938; Berry, 1941), and gall midges, Cecidomidae 

 (White, 1946, 1947, 1948). Of greater interest for present pur- 

 poses, however, are evidences of nuclear differences in histologi- 

 cally distinct somatic tissues. Comprehensive reviews of the oc- 

 currence of normal polyploidy in specific tissues of otherwise 

 diploid animals and plants are given by Berger (1941), Geitler 

 (1941), Huskins (1947, 1952), Schultz (1952), and Fankhauser 

 ( 1954 ) . Polyploid nuclei have been reported in vascular bundles 

 and epidermal structures of plants, in nematode muscle cells, in 

 ganglion cells of snails, and in various arthropod tissues. Similar 

 cases of somatic polyploidy have been reported in the kidney, 

 liver, and epidermis of amphibia, as well as in liver, vascular, and 

 tumor tissues in mammals. Tissue-specific haploidity is claimed 

 for the tail mesenchyme of frog larvae (Green, 1953) and for the 

 mesenchyme-forming micromeres of the sea urchin in which 



