REPRODUCTION 



single cell. This erotic division of labor is so impor- 

 tant that formerly it was universally ascribed to two 

 different cells. Recent accurate research, penetrating 

 into the smallest visible processes of fertilization, has 

 shown that the essential feature in the formation of a 

 fresh individual (the stem-cell) is the blending of equal 

 portions (hereditary parts) of the male and female nuclei ; 

 the caryoplasm of the two copulating cells is the vehicle 

 of heredity from the parents. The cytoplasm of the 

 cell-body, on the other hand, serves the purposes of 

 adaptation and nutrition. As a rule the cell-body of the 

 ovulum is very large, and is, as a food-store, very richly 

 provided with albumin, fat, and other nutritive matter 

 (food-yolk); while the cytoplasm of the sperm-cell is 

 very small, and generally forms a vibrating lash, with 

 which it moves along and seeks the ovum. 



In most of the plants the female and male cells are 

 produced by the same sprout, and in many of the lower 

 animals by one and the same person. This kind of 

 hermaphrodism in "individuals of the second order" is 

 called monoclinism ("one-beddedness"). In many of 

 the higher plants (monoecic stocks) and most of the 

 higher animals we have diclinism (" two-beddedness") 

 — in other words, the one sprout or person has only male, 

 and the other sprout or person only female, organs — this 

 is gonochorism of individuals of the second order. Mono- 

 clinism is generally associated with sedentary life (and 

 often necessary for it), and diclinism with free movement. 

 Adaptation to parasitic habits also favors monoclinism; 

 thus, the crabs, for instance, are for the most part 

 gonochoristic individuals, but the creeping crabs {cirri- 

 pedia), which have adopted sedentary (and to an extent 

 parasitic) habits, have become hermaphrodites in con- 

 sequence. Many intestinal parasites among the lower 

 animals (such as tape-worms, suctorial worms, wonder- 

 snails), which live isolated lives inside other animals, 



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