CANNON: Srupies IN PLant Hyprips 149 
I wish to call attention especially to number 6 of the above 
table, namely, to that form of irregularity in the distribution of 
the chromosomes by which a portion of them are thrown out of 
the nucleus, a portion only remaining. The result of this might 
be, as Juel suggests, that the nucleus of the tetrad would contain 
chromatin of pure descent, that is, chromatin derived from one 
and not from both parents. 
Guyer * has studied the spermatogenesis of hybrid pigeons and 
of hybrid cannas and found in both cannas and pigeons similar 
mitoses ; consequently it will be necessary to speak only of the 
mitoses in the hybrid pigeon. I shall quote direct (/. c. 312): 
“In the spermatogenesis of hybrid pigeons several abnormali- 
ties are manifested. These may be classified conveniently under 
three heads: (1) abnormalities in the structure of the spermato- 
zoa ; (2) abnormalities in mitoses; (3) degeneration of the ger- 
minal cells. Abnormalities in the spermatozoan structure were 
present in sterile hybrids, the most noticeable feature being a vari- 
cosity or swelling about the middle of the head. In tracing the 
development of the spermatozoa, this curious modification was 
found to be due apparently to a lack of development of the head ; 
the nucleus did not elongate completely as in normal spermato- 
genesis. Abnormalities in mitosis were marked in both fertile and 
sterile hybrids. Large numbers of multipolar spindles were pres- 
ent. These were usually of the tripolar type. Occasionally two 
distinct and separate spindles occurred in one cell. The sperma- 
tocytes of the first order were the cells that showed this phenom- 
enon to the greatest extent. In the normal pigeon the chromo- 
somes in the spermatogonia are sixteen in number end in the 
primary spermatocyte eight.. The latter are laid down in rings and 
each is evidently double. On the spermatogonia of the hybrid 
there were sixteen chromosomes and in the primary spermatocyte 
often more than eight. In the latter there may be several of the 
large double type and a number of smaller rings, or sixteen small 
ring chromosomes may occur. If sixteen rings were present, they 
Were usually located on two separate spindles, eight to each spindle. 
* Guyer, Spermatogenesis in Hybrid Pigeons. Science, i 11: 248, pe pr ; 
Some Notes on Hybridism, Variation and Irregularities in the Division of the Ger 
cell. Science, II, 15: 530. 1902. 
