254 PROBLEMS OF FERTILIZATION 



Loeb has shown to be effective activating factors in 

 the sea urchin. 



Authors who have attributed a directly activating 

 effect to changes in the physical state of the colloids 

 of the egg are Fischer and Ostwald (1905) and Heil- 

 brunn (1915); the latter author's results have been 

 reviewed previously (p. 153). The view that he main- 

 tains is "that the only physico-chemical effect which 

 all parthenogenetic agents possess in common is the pro- 

 duction of a gelatinization (or coagulation) within the 

 egg. Hence I regard this gelatinization (or coagulation) 

 as the direct cause of the initiation of development" 

 (1915, p. 191). In what sense, however, coagulation may 

 be considered to activate the egg is by no means clear; 

 the only demonstrable connection is between coagulation 

 and cell division, but the coagulation involved there is 

 strictly localized (p. 153) and not general. For the pro- 

 cess of membrane formation itself Heilbrunn (1913) has 

 a different explanation, viz., that it is produced by a 

 lowering of the surface tension of a pre-existing mem- 

 brane, which is then pushed away from the egg by the 

 internal forces which previously balanced its greater 

 tension. It is only by regarding membrane formation 

 as a mere epiphenomenon that the subsequent coagu- 

 lation can be treated as a primary activating factor. 

 However, the phenomenon of the primary cortical change 

 is too general to be treated in this fashion, and its 

 character in different animal groups is too varied for it 

 to be a mere phenomenon of decrease of surface tension. 

 The egg activated by a spermatozoon also coagulates in 

 the same sense, as Heilbrunn has shown by his measure- 

 ments, but Heilbrunn does not maintain that the sperms,- 



