FERTILISATION 



195 



take place, aud in the absence of these structures the piocess of cell 

 division makes no further progress, and the chromosomes finally 

 degenerate and break down. This experiment clearly pro\'es that 

 the sperm bring about profound alterations in the egg while still 

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

 of Stronf/loccntrotus are fertilised with the sperm of Adcrias, in 

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



n-r'T-T-T-,,,-'^ 



-«S^i^'^^-^- -^^^sWW^^'^^ ^^ ''I '' ' •'11 



a 







Fig. G1. — Tlie entiunce nf the sperniatozoiiii into tlie ejj'g (if 3V/v/s. 



Penetration of the sperinatozoiin in tlie egg of Xercis^ fifim sections : u, thirty- 

 seven minutes aftei' insemination ; /', c, <l, thiee stages fiom eggs killed 

 forty-eight and a half minutes aftei' insemination ; c, fifty-four minutes 

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

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

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

 (From Lillie's Prohlen'in of ['''rrtilifiitiiui, University of Chicago Press.) 



actual segmentation takes phrce unless the eggs receive further 

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



Meyerhof and Warburg in many of their experiments liave 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 ^ found that this is usually accompanied by an increased 

 liberation of heat. In eggs treated with weak solutions of KaC'l 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 



' Meyerhof, " Die Atmung der Seeigeleier (,S'. lirulin;) in reinen Ohloruati ium- 

 liisungen," Bionhein. Zeit., vol. xxxiii., 1911. 



