A Small Chromosome in Ascaris iiiegalocephala. 
123 
raales, tliat is 47^ males, is the one to which the most irai)ortaucc 
raust be attached, as the nuraber of worras found here in one horse 
was rauch greater than in other instances. It is ditficult to say 
whether these two series of percentages have any direct bearing on 
each other, as all the raales and feraales in one horse do nof neces- 
sarily come frora the sarae parent. They at least show that the 
percentage of raales in one horse and the percentage of eggs with 
a small chromosome in any one worm are both very variable 
(piantities. 
Interesting as it is to lind this small chromosonie in so large 
a Proportion of eggs, still the fact that it was never found in five 
worras and in so small a percentage in others, excludes the possibility 
of its representing any definite characters, unless its presence is mar- 
ked in many cases by a union with one of the long chroinosomes, 
to form some such complex as Mc Clung (’Oö) has described in 
Orthopteraus. If so, the point of union is not diseernible as in the 
Orthoptera, and the difficult}' of settling this question is almost 
insurmountable. An attempt was made to measure the chromosomes 
in many of the Hattest equatorial plates. They were drawn with 
the Camera lucida and the length of a line extending through the 
middle of the chromosome was very carefully measured off by means 
of thread and forceps. The Variation in the length of the four 
chromosomes is usually just as striking in the equatorial plates 
where the small chromosome is present, as where it is absent. Some- 
times one chromosome is longer than the other three, sometimes one 
shorter, while again two may be long and two short, or one long, 
two medium and one short In fact, every possible Variation is found, 
so that it is impossible to decide whether or not an extra element is 
attached to one end of one chromosome. These results do not Support 
those of Moxtgomekv (’08), where he says that it is always possible 
to group the four chromosomes into one long and one short })air. 
This Variation in length is almost to be ex])ected from the shape 
of the chromosomes (Fig. 1). They vary considerably in diameter, 
suggesting a dilference in degree of contraction, which would neces- 
sarily aflfect the length. 
In contrast to this indeterminate Variation, there are many eggs 
with the small chromosome, where one of the long chromosomes is 
so rauch shorter than the other three that the diflference appeals to 
the eye before raeasuring (Fig. 2). Such cases suggest Herla's ex- 
planation that the small chromosome is merely a fragment. It is 
