224 PLANT LIFE 



are watched under the microscope while the 

 sperms are swimming about them, they will 

 be seen, one by one, suddenly to change 

 their form they swell up, and at some one 

 spot on their surface they become " prickly." 

 This prickliness spreads with great rapidity 

 over the surface of the egg. The onset of 

 this curious appearance marks the entrance 

 of a sperm into the egg. The immediate effect 

 of that sperm on the egg protoplasm is to 

 render it not only no longer attractive to 

 the rest of the sperms, but actually poisonous 

 to them. An explanation is therefore at once 

 furnished as to how the entrance of more 

 than one sperm is prevented. The change is 

 a sudden one, resulting from the interaction 

 of the substance of the egg and sperm a 

 circumstance which sufficiently emphasises 

 the physiological difference existing between 

 them. Under unfavourable conditions, e. g. 

 badly aerated water, or by the addition of 

 certain substances to the water, the sudden- 

 ness of this reaction can be slowed down, and 

 then it may happen that more than one 

 sperm effects an entrance. But it seems to 

 be a general rule that if more than one of 

 them fuses with the nucleus of the egg, 

 either no further development takes place, 

 or monstrous embryos are produced which 

 commonly die during the earlier stages of 

 development. 



It is evident, then, that the act of sexual 

 fusion produces striking and immediate change 



