434 



The Life- Cycle of Cladocera. 



2. Parallel cultures to the above, when the parents are kept crowded to 

 the number of 10 in a glass and at a temperature of 10-17° C, produced 

 about 7 per cent, males and 10 per ceut. ephippial females. 



3. The crowding does not directly influence the supply of food, but appears 

 to act by the accumulation of excretory matter in the glasses. 



4. The parthenogenetic females kept isolated at 27° C. grow and repro- 

 duce more rapidly than those crowded at 10-17° C, and they store up 

 reserve material almost exclusively in the form of glycogen, while the 

 crowded parents at a lower temperature tend to store up fat instead of 

 glycogen and are inhibited in their growth. 



5. The storage of fat as opposed to glycogen is especially characteristic of 

 the males and ephippial females ; hence it is judged that the fat-storage 

 induced experimentally in the crowded parthenogenetic females at 10 -17° C. 

 is causally connected with the production by them of the sexual forms. 



6. We may conclude that the habit of glycogen-storage leads to rapid 

 growth and parthenogenesis, which is a form of discontinuous growth, while 

 the habit of fat-storage leads to inhibition of growth and sexual mode of 

 reproduction. 



7. In the higher Crustacea the act of growth and moulting is accompanied 

 by heaping up of glycogen in the liver storage-cells as opposed to fat, while 

 in the periods between moults fat-storage preponderates. 



8. Preponderant fat-storage in the liver is characteristic of female crabs 

 maturing their ovaries and of crabs infected by Sacculina, and in both these 

 cases growth is inhibited. 



9. We thus find that both in Cladocera and Decapoda growth on the one 

 hand, and sexual maturity on the other, are accompanied by a different type 

 of reserve storage, which is also distinct in the case of the male and female. 

 This is the physiological fact at the root of the antagonism between growth 

 and sex. 



10. Sexual reproduction is a reaction to conditions when continued growth 

 is disadvantageous or impossible. Sexual differentiation is an economy or 

 division of labour by which the female reproductive cell stores the material 

 for development and thereby loses the power of division, while the male cell 

 retains the power of division but relies on the female to supply the material 

 for development. 



