THE CYCLE OF LIFE 



387 



unfertilized egg ; the cells of the body had only half 

 the normal number of chromosomes. In some cases 

 the number seems to be normal, which may be due 

 to the fact that the ova began to develop under arti- 

 ficial stimulus before the ordinary reduction process 

 had occurred ; or to a subsequent restoration of the 

 reduced number ' by a process of auto-regulation ', as 

 is said to be the case in Delage's parthenogenetic sea- 

 urchin larvae. 



The general opinion of experts is thus summed up by 

 Professor E. B. Wilson. As 

 the ovum is much the 

 larger, it is beUeved to 

 furnish the initial capital 

 — including in some cases 

 a legacy of food-yolk — for 

 the early development of 

 the embryo. From both 

 parents ahke comes the 

 inherited organization which 

 has its seat (in part at least) 

 in the readily stainable 

 chromatin rods or chromo- 

 somes of the nucleus. From 

 the father comes a Uttle body, the centrosome, which 

 organizes the machinery of division by which the egg 

 splits up, and distributes the dual inheritance equally 

 between the daughter-cells. Besides bearing the paternal 

 inheritance, restoring the number of chromosomes to 

 the normal, introducing the centrosome (which serves as 

 'the weaver of the loom'), and acting as the normal 

 trigger-puUer which sets the egg a-going on the path- 



Pio. 61. — ^Diagram of a cell, l,the 

 nucleus ; 2, the chromosomes, 

 or readily stainable bodies in 

 the nucleus ; 3, the cell sub- 

 stance or cytoplasm showing 

 a reticular structure ; 4, the 

 cell-wall. 



