REPRODUCTION AND HEREDITY 149 



their sex as exhibited in the sperm- cells — an innate tendency 

 towards rapid motion and dissipation of energy, while the 

 larger, quieter, less conspicuous, less aggressive female 

 follows the tendency of the egg to grow excessively and to 

 store up food. It is, however, noteworthy that in the vast 

 majority of insects secondary sexual characters are not 

 conspicuously developed, and the problem remains why 

 these outward differences should be so unequally evident 

 in various members of the same order or family with regard 

 to sex ? We have seen reason for concluding that the sex of 

 an individual insect depends normally on the germinal 

 constitution of the egg (fertilised or unfertilised) whence it 

 has developed, while the existence of the gynandromorphs 

 and intersexes warns us that the normal development may, 

 on occasion, be disturbed or side-tracked through some 

 irregular behaviour of the multiplying cells. 



Secondar}^ sexual characters and modes of activity lead 

 us naturally to the subject of that behaviour before actual 

 pairing, wbJch is generally known as courtship. It will, 

 however, now be convenient to turn immediately to the 

 manner of growth of an insect from egg to adult, and then 

 to pass on to aspects of courtship in connection with a 

 general discussion on the family life of insects. 



