The Division of Labor. 33 



the name of eggs. But lying close to the egg- 

 cells is a gland, s, from which are sent other buds, 

 much smaller than the eggs. These ripen and fall 

 with the ripe eggs into the water of the body- 

 cavity. 



When these tiny particles and the eggs are set 

 free together in the water, they feel the same 

 attraction toward each other that the two uniting 

 cells of spirogyra felt, or the two protozoa when 

 they were so irresistibly drawn to unite with each 

 other. 



The egg-cell of the ascidian has not enough 

 vitality to develop unaided into an ascidian, 

 neither has this smaller cell. If like the two 

 protozoa they unite, however, the result can be 

 achieved. 



It would seem as though this complex ascidian 

 could not impress the image of all its parts upon 

 one set of cells, but that the great labor of pro- 

 ducing an ascidian must be shared; so it supplies 

 two sets of cells, which by uniting become able to 

 reproduce the parent form. 



The smaller particles are called sperm-cells and 

 represent the male element, while the egg-cells 

 form the female element. 



Free to move about in the body-cavity the sperm 

 and egg cells are attracted to each other; each 

 egg-cell is penetrated by a sperm-cell, and from this 

 union develops the young ascidian which appears 

 at X, wriggling about, unattached and free, in the 



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