WHY THE MULE IS INFERTILE 
When body cells divide there is no preliminary pairing of chromosomes. 
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But when germ 
cells are formed each chromosome pairs with its mate as a necessary preliminary to division. 
In the case of the pure species this is a regular and orderly process as shown in the figure 
to the left. 
figure to the right. 
But in the germ cell divisions of the mule this is impossible as shown in the 
One trouble is that the hybrid has received nineteen chromosomes 
from his dam, a mare, and thirty-two from his sire, a jack; and when the chromosomes 
come to pair off there are not enough of the right kinds to pair. 
In addition there is an 
incompatibility between those ‘‘pairs’’ that are present and pairing is difficult or incom- 
plete. 
The whole machinery of the cell is, therefore, upset and the cell itself destroyed. 
Camera lucida drawing, enlarged 3,000 times, from J. E. Wodsedalek (Biol. Bull., XXX, 
pl. Dy Gia 35) 
faulty observation, or as due to wrong 
interpretation of facts. The cases re- 
ported are so rare that this is not a 
difficult undertaking. 
2. The germ glands, as well as the 
secretions discharged therefrom, of the 
hybrids are studied histologically and 
cytologically. These studies indicate a 
deep-seated derangement of the cell 
divisions which would, in normal, fertile 
animals, give rise to the fully developed 
germ cells. 
SOME STRONG EVIDENCE 
1. As to the first mentioned line of 
attack calculated entirely to disprove 
fertility among mules, 7. e., throwing all 
reported cases out of court as errors, 
it must be said that the facts as shown 
above in some cases are too strongly 
supported to be regarded as only 
fiction, and to be cast lightly aside; some 
way of “‘explaining’’ such cases is neces- 
sary. Those unwilling to give credence 
to the stories of fertile female mules, 
explain the “supposed cases” in one of 
two ways. 
(a) The female may have produced a 
hybrid colt, but the real nature of this 
fertile female may not be known. 
498 
Frequently horses of mixed breeding 
are seen which exhibit asinine traits of 
character, both externally and in dis- 
position. If a female of this nature 
became pregnant, she might well be 
mistaken for a fertile mule. Such a 
case is doubtless the well-known instance 
in the Acclimatization Gardens in 
Paris. A female—supposedly a mule— 
produced foals when mated with both 
the horse and the ass. She was sold 
to the Gardens by some Algerian natives 
who alleged her to be a mule. It 
developed later that it was extremely 
doubtful whether the animal was a mule. 
The particulars of her parentage, etc., 
are utterly unknown, except as narrated 
by the Algerian horse traders and there 
were, aS shown in a photograph repro- 
duced by Tegetmeier and Sutherland, 
but vague suggestions of mule-like 
character about her. Her foals by an 
ass appeared to be ordinary mules and 
were sterile; her progeny by the stallion 
were horses which proved fertile. 
In fact it is quite possible that the 
Sullivan case from Weed, Cal. (Fig. 6), 
belongs in this category. On examining 
Fig. 6 many readers will doubtless at 
