28 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



stances adult animals. This interesting result may 

 be obtained by adding certain salts to the sea-water 

 in which the eggs of marine animals normally de- 

 velop, or in the case of the frog by puncturing with 

 a needle the outer layer of the unfertilized egg. 

 Professor Loeb, who inaugurated these experiments, 

 is of the opinion that oxidation is thereby stimu- 

 lated, which is followed by an accelerated protoplas- 

 mic activity that initiates a normal development of 

 these ova without the process of fertilization. If 

 a spermatozoon enters the ovum before the polar 

 bodies are extruded, the spermatozoon remains inert 

 within the cell until maturation is completed. The 

 ovum, thus reinforced, enters upon an aggressive 

 growth, a phenomenon quite in contrast with its 

 preceding history. 



Fig. 5. Cleavage in egg of frog, i to 16 cell stage. 



Segmentation or Cleavage. Following fertiliza- 

 tion the ovum multiplies rapidly by mitosis. The 



