On Morphological Difiference of the Chromosomes of Ascaris megaloceph. 71 
to reason that the bendings of the chromosomes above or below the 
plane of the paper, which are represented unshaded, are longer 
than the drawings seem to represent them, and that it is only after 
a carefiil ocular estimation of the heights and depths of such bends 
that I have ventured to decide in each case which are two longer 
chromosomes. In some of the cells the length difl'erence is very 
considerable. 
We couclude from this series of 35 examples, selected entirely 
in the order of their fiuding and so picked at random, that in the 
great majority of cases, 32 out of 35, the four chromosomes com- 
pose one pair of longer elements and one pair of shorter. And, con- 
sequently, on comparison with the observations previously related, 
that in each pair one element is paterual and the other maternal. 
Fignres 36 — 42, Fl. 1, illustrate a few equatorial plates of the 
second cleavage, and in these also the elements of the larger ])air 
are indicated by the letter »x«. In several of these cases the lar- 
ger chromosomes cannot be distiuguished with certainty from the 
smaller, but I believe the difficulty here is due to the chromosome.s 
of this second cleavage beiug usually more slender and more twis- 
ted than those of the first, which reuders less certain the estimation 
of their lengths. 
A study of the cleavage chromosomes shown in Flate 1 would 
show that there are no constaut form dififerences. In general the 
shorter chromosomes have fewer angles than the longer, a phenomenon 
well referable to the relative pressure conditions exerted upon the 
chromosomes while confined within the membranes of the pronuclei. 
The smallest chromosome of all is very frequently hook-shaped and 
the other one of the smaller pair often U-shaped, while the longer 
ones have usually two or three angles each, but none of these diffe- 
rences in form appear to be constant. 
The morphological chromosome difl'erence in this species is there- 
fore one of volume or length but not of form. 
5. General Considerations. 
We have found that the sperm introduces two chromosomes that 
are constantly of slightly unequal volume, and that the egg, wheu the 
two polar bodies are cut off, retains two also of slightly unequal volume. 
Further, from each pronucleus preceeds constantly one longer and one 
shorter chromosome; and in the first cleavage spindle there are distin- 
guishable in the great majority of cases, 32 out of 35, two longer 
