238 GENERAL BIOLOGY 



which are laid within the soft and richly nourished 

 larvae of other insects, undergo a division which is 

 rather fragmentation, than segmentation; for it 

 results in the development not of a single embryo but 

 of many embryos. The parts into which the nucleus 

 divides develop separately as indicated diagrammatically 

 in figure 190, each becoming a complete embryo, and 

 growing later to adult estate. A significant feature of de- 

 velopment by this method is that all the individuals de- 

 veloped from one egg are of the same sex. 



Reproductive methods in general. — Sufficient illustrations 

 have now been before us to show that there is one sexual 

 method of reproduction, fairly uniform and consistent 

 throughout the organic world, but that there are many 

 asexual methods, and that these latter are most diverse. 

 The former is uniform in its fundamentals in all kinds 

 of environment; the latter are uniform in nothing, and they 

 show the most significant relations to conditions of life. 



The unity of the organic world is hardly more manifest 

 in the possession of protoplasm, than in the production of 

 gametes, and in the fusion of these in fertihzation. The 

 primary differentiation of multicellular bodies is into germ 

 plasm and body plasm. This is even older than the 

 differentiation between plants and animals. But the 

 secondary sexual characters show as great diversity as do 

 asexual reproductive phenomena: these are the after 

 thoughts of reproduction: these are the special means 

 adopted by special groups. How different are even sperm- 

 aries and ovaries in the stoneworts and in the liverworts ! 

 How lacking in common features are the reproductive organs 

 of an earthworm and a salamander ! All these have been 

 more recently developed, along independent lines, in accord- 

 ance with the tendencies and in adaptation to the needs 

 of the different groups in which they are found. 



