246 PROBLEMS OF FERTILIZATION 



in their purpose of securing a substance that will act 

 on eggs of the same species. But on the other hand 

 watery extracts of sperm may be highly cytolytic to 

 ova of other species, especially of different classes or 

 phyla; there is, however, no tissue specificity in this, 

 for blood or tissue exudates may have the same effect. 

 It is therefore obvious that we must accept the nega- 

 tive result within the species as showing that cytol- 

 ysins borne by the sperm have no cytolytic function in 

 normal fertilization; they act only on foreign species. 



Loeb's theory is based mainly on the study of the 

 sea urchin. However firm may be our conviction that 

 the fundamental phenomena of activation must be the 

 same throughout the animal kingdom, yet we must not 

 fail to realize that each species will show its own pecul- 

 iar aspects. In the case of the sea urchin one of these 

 is the sharp separation between the two stages on which 

 Loeb lays so much emphasis. In most other forms, 

 e.g., starfish, annelids, frog, the activation process 

 appears continuous, though capable of arrest at vari- 

 ous stages. In the case of the frog, however, Herlant 

 (1913) has shown that a separation of two phases 

 similar in principle to that of the sea urchin may 

 readily be recognized. 



R. S. Lillie (1908, 1915) has examined certain 

 quantitative aspects of activation with much greater 

 precision in the case of the starfish, and from such 

 determinations different points of view naturally arise. 

 He has determined that definitely timed exposures to 

 supranormal temperatures constitute an almost perfect 

 method for producing parthenogenesis in the starfish. 

 This is the simplest possible method of studying the 



