REPRODUCTION AND HEREDITY 137 



important limitation of the evidence must be admitted. 

 All the characters whose inheritance by means of the 

 chromosomes has been clearly demonstrated, are detailed 

 characters — varietal or specific. It is extremely likely that 

 the factors for the more fundamental characters — those, 

 for example, which distinguish a fly from a moth or a bee — 

 are also situated in the chromosomes, but some students of 

 the problems of heredity believe it possible that these may 

 reside rather in the cytoplasm of the germ-cells, especially 

 perhaps in the egg-substance. In connection with this 

 possibility, it is of interest to note that definite bodies 

 granular or rod- like (chromidia) and also reticulate (" Golgi- 

 bodies "), have been now observed in the body-cells and 

 germ-cells of many insects as of other animals. In some 

 cases these bodies appear to undergo a definite and regular 

 process of division when the cells are dividing, so that their 

 individuality and continuity may be inferred. Possibly, as 

 some students of the subject have supposed, they are 

 nuclear in origin, and may be the agents by means of 

 which the nucleus influences the substance of the cell. 

 For information on these bodies reference may be made 

 to the writings of Wilson (1925) and J. B. Gatenby 

 (1917-19). 



So far we have considered the working of inheritance 

 and reproduction among insects along the usual lines of the 

 sexual process common to the great groups of animals 

 generally, the new individual developing from the fertilised 

 egg. It is well known, however, that in many animals 

 cases of development from an unfertilised egg occur, some- 

 times exceptionally, and sometimes as part of the regular 

 life-cycle of the creature. Study of the reproduction of 

 insects shows some of the most remarkable and interesting 

 examples of this virgin- generation (parthenogenesis) that 

 the animal kingdom affords. 



Not a few female moths that had never paired with a 

 male have been known on occasion to lay eggs from which 

 caterpillars were hatched to be in due course transformed 

 into moths ; the Common Silkworm {Bomhyx mori) and 



