398 PHILOSOPHY OF ZOOLOGY. 
animals which produce many young at a birth, never reach 
the uterus, but are retained im the remote extremities of 
the horns, where they are brought to maturity. But the 
following experiment, which has been repeated by many 
observers, puts the subject beyond a doubt. When one 
of the oviducts is divided, as has been tried with rabbits, 
the corresponding ovarium, though capable of producing 
corpora lutea, cannot generate a fetus or impregnated 
germ *, How the sperm penetrates the small mouths of 
the oviducts to be conveyed to the ovarium, will not likely 
be soon determined. A small portion probably suffices to 
produce the effect, as is known to be the case with ovipa- 
rous animals and plants. It is not ascertained in the case 
of those animals which produce but one ata birth, whether 
the ovaria contribute the germs irregularly or in succession. 
But it is probable that, in the case of twins +, and where 
more males than one are admitted, as in the dog, both 
ovaria contribute their share. 

* See some interesting experiments in reference to this subject by Dr 
Harcuton, Phil. Trans. 1797, p. 159.3; and by Mr Cruicxsnansxs, ib. 
p- 197. 
+ There is a very curious instance of a white woman producing twins, 
one white, and the other a negro, in Dr Extrotson’s valuable Translation 
of Biumengacn’s “ Institutions of Physiology,” p. 331.—‘¢ A white wo- 
man of very gay character left her husband, and some time afterwards 
returned pregnant to her parish, and was delivered in the work-house of 
twins,”—** one of which,” says Mr Brackatier (of Weybridge), in an 
account which he very handsomely sent me, ‘¢ was born of a darker 
colour than I have usually observed the infants of negroes in the West 
Indies; the hair quite black, with the woolly appearance usual to them, 
with nose flat and lips thick ; the second child had all the common appear- 
ances of white children.” 2 
Where foetuses occur with additional parts, such as a double head, or 
where two bodies are united at a particular part, as in the celebrated Hun- 
garian sisters, has the monstrosity been produced by the evolution of a 
double ovum, or by the union of two ovain the uterus? Many circum. 
stances countenance the latter supposition. 
