88 JACQUES LOEB. 



responsible for the sudden increase in the rate of oxidations after 

 artificial or natural membrane formation. Since fertilization by 

 sperm is accompanied by a membrane formation and followed by 

 the same increase in the rate of oxidations as is artificial membrane 

 formation by butyric acid, it is probable that the alteration of the 

 surface (underlying membrane formation) is also the cause for 

 the increase in the rate of oxidations in the process of natural 

 fertilization. 



2. The writer has time and again stated that the formation or 

 non-formation of the fertilization membrane is of only secondary 

 importance; what matters are the physicochemical changes 

 which underlie the membrane formation and which are responsible 

 for the sudden rise in the rate of oxidations of the sea urchin egg 

 after artificial or natural membrane formation; and which may 

 even occur when for some reason the fertilization membrane is 

 modified or when its formation is entirely suppressed. There is 

 no doubt that in the writer's first experiments with the purely 

 osmotic method, the fertilization membrane was often very 

 indistinct or in some cases even completely lacking, while 

 nevertheless the enormous increase in the rate of oxidations and 

 development to the pluteus stage ensued.^ 



It is possible to modify the surface of the unfertilized egg in 

 such a way that if it is later fertilized by sperm the abnormal 

 character of the membrane formed, or the abnormal conditions 

 of the surface, may lead to the death of the egg. The writer 

 described such a case in 1909.^ When the unfertilized eggs of 

 Strongylocentrotus were treated for five minutes with a hyper- 

 alkaline solution of NaCl (50 c.c. w/2 NaCl + 1.0 c.c. N/io 

 NaOH) and then transferred to normal sea water to which sperm 

 was added, the eggs were all fertilized but apparently without 

 membrane formation, though in reality probably with a tightly 

 fitting membrane. They all segmented but perished in the 

 blastula or gastrula stage. When, however, the eggs were not 

 fertilized immediately after the treatment with alkali but after 



1 The literature of the subject can be found in the writer's recent book on 

 "Artificial Parthenogenesis and Fertilization," Chicago, 1913. 



2 Loeb, "Die chemische Entwicklungserregung des tierischen Eies," Berlin, 1909, 

 p. 117. 



