142 SECRETS OF EARTH AND SEA 



removed in this way by transfusion or injection of 

 important fluids from the one into the other. 



We must not lose sight of the fact, in the midst of 

 these various and diverging observations about the 

 fertilization of the ova of one species by sperms of 

 another species, that there is such a thing as " partheno- 

 genesis," or virgin-birth. In some of the insects and 

 lower forms of animals the egg-cell habitually and 

 regularly develops and gives rise to a new individual 

 without being fertilized at all. And in other cases by 

 special treatment, such as rubbing with a brush, or in the 

 case of marine animals by addition of certain salts to the 

 water in which the eggs are floating — or, again, in the 

 case of the eggs of the common frog by gently scratching 

 them with a needle— the eggs which usually and regularly 

 require to be penetrated by and fused with a spermatozoon 

 or sperm-filament before they will develop, proceed to 

 develop into complete new individuals without the action 

 upon them of any spermatozoon. In such marine animals 

 as the sea-urchins or sea-eggs it has been found that the 

 eggs deposited in pure sea-water, though they would die 

 and decompose if left there alone, can be made to develop 

 and proceed on their growth by the addition to the sea- 

 water of the sperm filaments of a star-fish (the feather 

 star or comatula). The spermatozoa or sperm-filaments 

 do not, however, in this case fuse with the egg-cells. 

 They mechanically pierce the egg-coat, but contribute 

 no substance to the embryo into which the egg develops. 

 They have merely served, like the scratch of a needle on 

 the frog's egg and the brushing of insects' eggs, to start 

 the egg on its growth, to " stimulate " it and set changes 

 going. It appears thus that the fertilizing sperm-filaments 

 of organisms generally have two separate and very im- 

 portant influences upon the egg-cells with which they 

 fuse. The one is to stimulate the egg and start the 



