500 The Journal 
fostering a foal born of a mare—perhaps 
one lacking maternal instincts. In 
herds of horses and mules it might easily 
happen that a milking mule should 
adopt an orphan colt and give every 
appearance of being the colt’s true 
mother. 
2. Facts from the second line of 
study, 7. e., examination of the cell 
processes going on within the testis, 
and of the nature of the seminal dis- 
charge, will now be considered. Cossar 
Ewart was among the first to subject 
the seminal fluid of equine hybrids to 
microscopic inspection. His hybrids 
were produced by use of a Burchell 
zebra male on pony mares.! The male 
“Zebroids” thus formed were unable to 
beget offspring in the many mares to 
which they were put, though, as is true 
of male mules produced in the ordinary 
way, their behavior gave every reason 
to suppose that they were breeders. In 
the discussion of his work, Ewart 
repeatedly mentions seeing incompletely 
formed spermatozoa which were “hardly 
at all motile due to the tail being only 
about twice as long as the head, while 
in the normal horse and zebra it is fully 
eight to ten times the length of the 
head.”” This seems like a case of 
arrested development. Ewart inter- 
preted this lack of motility as evidence 
that these imperfect sperm cells were 
unable to make any headway against 
the outward currents which exist in the 
generative tract of the female. As a 
result they never reached the ovum, 
were of no use, and the zebroid was 
sterile. 
Stephan in 1902 reported some studies 
on the structure of mule testes. Some of 
his material was taken from castration 
operations and some from animals 
which had died. His studies were 
histological rather than cytological. 
He reports an almost complete absence 
of seminiferous tubules, a great exag- 
geration of “parenchyma”’ tissue, and 
many other unusual features. 
In 1905 appeared Iwanoff’s ‘‘Unter- 
suchungen uber die Ursachen der Un- 
fruchtbarkeit von Zebroiden.”’ 
of Heredity 
In point of material his work is com- 
parable with Ewart’s, but in results it is 
different. 
Iwanoff worked with two male ze- 
broids, one 4 and one 5 years old. 
Microscopic examination of the seminal 
discharge showed complete lack of 
spermatozoa, but many round, hard, 
glancing, refractory, glass-like bodies 
were present. ‘“‘In these cases one can- 
not speak of degenerate or undeveloped 
sperm cells. Ewart probably mistook 
the round glass-like bodies with Brow- 
nian movement for sperm cells. How 
Ewart’s observation of a tail twice as 
long as the head, in the semen of his 
hybrid, is to be explained, I cannot say.” 
Suchtet (96), as the result of his work 
on mule testes, also concludes that the 
spermatozoids were replaced by ‘“‘little 
round, brilliant, glassy bodies.” 
The presence of these round refractory 
bodies in the semen cannot be gainsaid, 
but it is questionable if they should be 
interpreted as ‘replacing’? the sper- 
matozoa. These bodies are probably 
merely masses of hard albumen, and 
not cellular bodies at all. Similar 
bodies may be seen in the semen of 
normal sheep, swine and rabbits, in 
which there is an abundance of live and 
perfect spermatozoa. After long stand- 
ing these bodies seem to absorb moist- 
ure, increase in size, lose their refractory 
properties and disappear. It is possible 
that the testes of the mule play little or 
no part in furnishing the seminal dis- 
charge, but that it is secreted by the 
accessory glands of the generative tract. 
DEGENERATIVE CHANGES 
Iwanoff also made some observations 
on the histological structure of the testis 
of the mule. He found tubules of 
greatly reduced diameter, comparable 
to those seen in sexually immature 
stallions. He reports excessive numbers 
of Sertoli cells, many degenerative, as 
well as degenerative spermatogonia. 
He also notes the presence of white 
leucocytes within the tubules, which, to 
his mind, play a part in the degenerative 
processes going on there. These obser- 
‘For an account of the production of zebra hybrids see “The Grevy Zebra as a Domestic 
Animal,’’ by George M. Rommell. 
November, 1913. 
American Breeders’ Magazine, Vol. 1V, No. 3, pp. 129-139, 
