195 



take place, and in the absence of these structures the process of cell 

 division makes no further progress, and the chromosomes finally 

 degenerate and break down. This experiment clearly proves that 

 the sperm bring about profound alterations in the egg while still 

 external to the egg-membrane. Loeb has shown that when the eggs 

 of Stronglocentrotus are fertilised with the sperm of Asterias, in 

 hyper-alkaline sea-water, they only form fertilisation membranes ; no 



J> 



FIG. 61. The entrance of the spermatozoon into the egg of Nereis. 



Penetration of the spermatozoon in the egg of Nereis, from sections : a, thirty- 

 seven minutes after insemination ; b, c, </,. three stages from eggs killed 

 forty-eight and a half minutes after insemination ; e, fifty-four minutes 

 after insemination ; the head of the spermatozoon now entirely within the 

 egg is contracting while the middle-piece of the spermatozoon remains on 

 the egg-membrane ; it never enters the egg ; the tail also remains outside. 

 (From Lillie's Problems of fertilisation, University of Chicago Press.) 



actual segmentation takes place unless the eggs receive further 

 treatment so that artificial parthenogenesis is induced (see p. 236). 



Meyerhof and Warburg in many of their experiments have shown 

 that any injury or cytolysis of the egg-membrane is invariably 

 followed by a great increase in the oxygen consumption of these eggs. 

 Meyerhof 1 found that this is usually accompanied by an increased 

 liberation of heat. In eggs treated with weak solutions of NaCl in 

 which the normal condition of the cell wall is destroyed in the 

 absence of Ca and K ions, the rise of oxygen consumption was five 



1 Meyerhof, " Die Atmung der Seeigeleier (S. lividus) in reinen Chlornatrium- 

 losungen," Biochem. Zeit., vol. xxxiii., 1911. 



