302 



GENERAL BIOLOGY 



eggs and sperms, contain half the number of chromosomes 

 that are found in the cells of the sporophyte. Thus, reduc- 

 tion and fertilization are widely separated in point of time. 

 Two divisions of the spore mother cell with only one splitting 

 of the chromosomes, result in these cells issuing with the half 



Maturing divisions 

 of the sperm cells Sperms 



Eggs 



Actual 

 number of 

 somatic 

 chromo- 

 Zygotes somes 



Lygaeus 



Anasa 



FIG. 179. Diagram illustrating the behavior of the "accessory," 

 sex-accompanying chromosome in fertilization (after Wilson). 

 For the sake of clearness, but four other chromosomes are 

 shov/n, and these four diagrammatically ; accessory (x) , solid 

 black. 



number in each, just as in the egg and sperm mother cells 

 of the higher animals. If % represent the number of chromo- 

 somes in the sex cells, these relations may be expressed by 

 the formula: 



( x J"lZygote (ax) The new individual ( 2 x) f sperm (x) 



W J I egg (x' 



gjjZygote, Sporophyte (zx) Spores (x) G ^ m t e ^? x) { | perm j 



Differentiation of the cytoplasm of the egg. There is also 

 defmiteness of organization in the cytoplasm of the egg. 

 Conklin has shown that in the egg of the ascidian Cynthia 

 there are three kinds of protoplasm that are quite different 



