178 



FERNANDUS PAYNE. 



I have not been able to follow the history of the differential 

 chromosomes during the growth period. A plasmosome is 

 present. Sometimes it stains perfectly black but again it may 

 stain much as the cytoplasm does. If the latter, a number of 

 chromatin bodies can be seen embedded in it. As I have fol- 

 lowed the history of the plasmosome and its relation to the dif- 

 ferential chromosomes in Prio7iidus it seems very probable that 

 here, too, in Acholla the differential chromosomes are embedded 

 in the plasmosome during the growth period. 



Polar view of the Side view of the Two classes of Reduced number Male and female 



first division second division spermatozoa. of chromosomes chromosome 



metaphase. anaphase. in the egg. groups. 



Fig. 3. 



Fig. 3 gives a diagrammatic representation of what occurs in 

 maturation and fertilization. 



Only a few years ago maturation meant a reduction to one 

 half ; the number of oogonial and spermatogonia! chromosomes 

 were thought to be the same in each species and this number an 

 even one. Even as late as 1900, Wilson in " The Cell in Develop- 

 ment and Inheritance " writes as follows : " Van Beneden's epoch- 

 making discovery that the nuclei of the conjugating germ-cells 

 contain each one half the number of chromosomes characteristic 

 of the body-cells has now been extended to so many plants and 

 animals that it may probably be regarded as a universal law of 

 development," Those who believe that the odd chromosome is 

 merely a delusion in the minds of a few investigators still cling to 

 the universality of Van Beneden's law. However, the law is no 

 longer of universal application. Not only the odd chromosome 

 but a number of other irregularities have been recently described. 



