54 



CHEMODIFFERENTIATION 



/sm. 1 



Fig. 19. a: egg of Tubifex, divided into two equivalent cells (7 and 

 II). Animal (an) and vegetative {veg) pole-plasm are both halved; 

 &: a similar ^^% during cleavage, two first {l.soin.I, LsomJI) and 

 two second somatoblasts i2.soni.I^ 2.som.II) have been formed; 

 c: the result is a double monster (so-called duplicitas cruciata) 

 with two pairs of germ-bands (7 and 77). After Penners. 



(Fig. 19c). This shows clearly that the presence of pole-plasm 

 really is the factor to which the cells owe the potency to form 

 an embryo, or, in other words, the factor that determines them 

 to form an embryo. Therefore, the pole-plasm is a real determin- 

 ing substance. 



