A Small Chromosome in Ascaris megalocephala. 
Ry 
Alice M. Boring. 
(From the Zoological Institute, Würzbnrg.) 
Witli plate X. 
lu 1894 , Herla iiieiitioued and figured a small fifth chromosome 
tbund in the eggs of two worms of Ascaris megalocephala hivalens. 
In the majority of these eggs, he found one of the larger chromo- 
sctmes markedly shorter than the other three, and suggested that the 
small one was a piece broken off from this chromosome. In a few 
eggs, he found the small chromosome where the four others were 
of normal length, and these, he thought, might be disi)erm eggs, 
fertilized bj' one hivalens and one imiralens Spermatozoon. 
Prof. Boveri had noticed this small chromosome from time to 
tune in his „Ismr/s-preparations, and had figured it once in a two 
cell Stage (’ 99 ). At the beginning of the wdnter semester 1908 — 09 , 
he observed it again in large numbers of eggs in the preparations 
from one w<»rm where the four chromosomes seemed to be of nor- 
mal size, and suggested that I make a careful study of the frequency, 
size, and possible function of this small chromosome. Preparations 
of the eggs from a second worm taken from the same horse showed 
the small chromosome in 60 out ot 135 equatorial plates of the first 
cleavage spindle. At first, all the evidence seemed to point toward 
its Corning exclusively from the Spermatozoon, and this together with 
the fact that it was found in about one half of the eggs, suggested 
the possibility that it might function as a sex determinant, like the 
heterochromosome of insects. Closer study has thrown rauch doubt 
on this hypothesis, but has offered no (»ther satisfactor}' explanation. 
