EGG ACTIVATION 217 



process for activation. Consequently, eggs may be regarded in the following 

 light: Some eggs are self-activating and develop spontaneously, while others 

 require sperm activation before development is initiated. However, the dif- 

 ferences between these two types of eggs may not be as real as it appears, for 

 it is probable that subtle changes in the environment of the so-called self- 

 activating or parthenogenetic eggs are sufficient to activate them, whereas in 

 those eggs which require fertilization a strong, abrupt, stimulus is requisite 

 to extricate them from their blocked condition and to start development. This 

 idea is enhanced by the information obtained from the methods employed 

 in the studies on artificial activation of the egg of different animal species. 



2. Artificial Activation of the Egg 

 a. Object of Studies in Artificial Parthenogenesis 



"The ultimate goal in the study of artificial parthenogenesis is the discovery 

 of the chemical and physical forces which are assumed to cause the initiation 

 of development" (Heilbrunn, '13). A brief resume of some of the results ob- 

 tained in the studies on artificial activation of the egg is considered in the 

 following paragraphs. 



b. Some of the Procedures Used in Artificial Activation of the Egg 



Tichomiroff, 1885 (Morgan, '27, p. 538), stated that eggs from virgin 

 silkworm moths could be activated by rubbing or by treatment with sulfuric 

 acid. Somewhat later Mead, 1896-1897, published results of studies on arti- 

 ficial parthenogenesis in the annelid worm, Chaetopterus. The egg of this 

 worm has the germinal vesicle intact when it is deposited in sea water. Almost 

 immediately after entrance into sea water, the germinal vesicle breaks down, 

 and the chromatin proceeds to form the spindle for the first maturation 

 division. At this point, however, it stops and awaits the entrance of the sperm 

 for further activation. Thus, the immersion of the Chaetopterus egg in sea 

 water under normal spawning conditions partially activates the egg (Mead, 

 1897). Mead attempted by artificial means to complete this activation initi- 

 ated by the sea water. In doing so, he took eggs from normal sea water, 

 which thus had the first polar spindle, and placed them in sea water to which 

 V4 to Vi per cent of potassium chloride had been added. Eggs thus treated 

 proceeded to form normal polar bodies and the beginnings of the first cleavage 

 occurred. Development ceased, however, at this point. These eggs were further 

 activated, but not completely activated. Two steps in partial activation are 

 here demonstrated: 



( 1 ) When the egg is spawned into sea water, the nuclear membrane breaks 

 down and the first polar spindle is formed; and 



(2) by the immersion in hypertonic sea water the first and second matura- 

 tion divisions occur, and the first cleavage begins. 



