NEOPLASTIC ABNORMAL GROWTH 245 



evokes alterations in avian tissue of molecular structures related in some 

 degree to those which occur spontaneously and transmit the disease. 



Cytoplasmic Control of Inherited Cellular Traits 



Since the early work in cytology of Roux and Weismann, evidence 

 has been available that constituents of cytoplasm play some role in the 

 development of the cell. The original experiments prove that removal 

 of particular regions of the ooplasm of the unsegmented egg without 

 injury to or disturbance of the nucleus is followed by corresponding 

 defects in the resultant embryos and larvae. This was taken to prove the 

 definite prelocalization in the cytoplasm of the unsegmented egg and 

 specification of the blastomeres due to the nature of the specific cyto- 

 plasmic materials which they receive during cleavage. This view was 

 further supported by the classic studies of the Spemann school on the 

 organizer substances. More recently, Sturtevant (104) examined the 

 evidence on the inheritance of dextral and sinistral coiling in the gas- 

 tropods and found that the eggs of a sinistral individual produce sinis- 

 tral offspring even if fertilized by sperm carrying dextral dominant 

 factor. J. A. Moore ( 105) showed that the cleavage rate of echinoderms 

 is a function of the cytoplasm, and E. B. Harvey (106) advanced evi- 

 dence that in the parthenogenetic merogony of enucleated egg frag- 

 ments chromatin plays only a minor role in early development. 



The experiments of Lindegren, previously mentioned, on the meli- 

 biose-splitting enzyme in yeast formed under the control of a specific 

 gene, are important. Once formed, the enzyme is produced as long as 

 the substrate is present, even in the absence of the active allele of the 

 gene which produced it. Beadle (25) draws an interesting analogy be- 

 tween this observation and the formation of pepsin from pepsinogen. 



Michaelis (107) studied the plant Epilobium and showed that recip- 

 rocal crosses between species and different races of single species show 

 differences between hybrids of first generation and behavior on back- 

 cross, indicating that cytoplasmic entities transmitted through the egg 

 are involved and depend upon the nuclear constitution of the plant in 

 which they are found. What is normal in plants of one genetic constitu- 

 tion is abnormal in those of another. 



Kiihn and Plagge (108) showed that the eggs of Ephestia, homozy- 

 gous for the a allele of the Aa gene pair, carry a hormone which requires 

 the A allele for its production and which disappears in subsequent gen- 

 erations. 



