58 BULLETIN: MUSEUM. OF COMPARATIVE ZOOLOGY. 
PaGeE. 
Ill. Discussion . ee : ; : : : 95 
A. Synapsis and the raelimmetiicn! aieieiaee : : ‘ : 95 
a. Results from Orthoptera : ‘ ; : : : 95 
b. Recent work on synapsis . ‘ : , : 5 98 
B. Individuality : : : : . 105 
a. Constancy of Hee cetombhomtee = 3 ; 5 eel05 
1. Constancy in number s ‘ ‘ : : 4 POS 
2. Constancy in size and shape . : : y Te eVLOG 
b. Persistent organization of, chromosomes : ; Pagers fil) 
1. The selected chromosomes ‘ , : , < EEG 
2. The heterochromosomes . = : j : 111 
3. Plasmosomes and nucleoli. . , : ee 
4. Persistence of chromosomes between “ines : oy Sule 
C. Chromosomes and heredity . 7 L ; . ; i ts 
a. Mendelism and maturation . é : : : ne eo slaks) 
b. Some experimental evidence . : : : ? of 122 
D. Summary of conclusions ; : : : : . 125 
IV. Bibliography : : : E ‘ ; : ; : a oL26 
V. Explanation of plates : : : : : ‘ , A ley 
I. INTRODUCTION. 
A. OUTLINE OF THE PROBLEMS. 
Two of the most important subjects which have claimed the atten- 
tion of cytologists for many years are the two named in the subtitle 
of this paper. Every species of animals and plants is thought to have 
a definite number of chromosomes, which is characteristic for the 
species. In the process of maturation this typical, or diploid, number 
becomes reduced so that each functional gamete contains only half 
that number, the haploid number. It is generally believed that the 
process of reduction is initiated by a pairing of the chromosomes in 
the prophase of the first maturation division. It is also generally 
admitted that of the two chromosomes which united to form a single 
pair, one has been derived from the maternal, and the other from the 
paternal ancestor, and that these become separated again at one of the 
two maturation divisions. But there has been a considerable amount 
of disagreement as to how the pairing of the chromosomes takes place, 
and also differences of opinion as to which of the two maturation divi- 
sions results in their separation. 
As to the process by which the pairing of chromosomes is accom_ 
