PHYSIOLOGY OF BREEDING. 
325 
already mentioned, a third is subsequently developed by the 
growing requirements of the foetus, this being situated 
between the other and older membranes, and having the 
office of originating the heart and blood-vessels. This third 
membrane would appear to be the joint production of the 
other two, from the circumstance of its contributing a set of 
organs equally necessary to both the external and internal 
parts of the body. If this be so, it appears to me an addi- 
tional reason for disputing Mr. Orton’s position, that “ the 
respective parents contribute certain portions of the off- 
spring, ” and a powerful argument in favour of the theory of 
their united action and common influence over every part of 
the foetus. But I do not for a moment infer that each parent 
exercises this influence in exactly equal proportions. 
It may be further remarked, that Mr. Orton’s experiments, 
so far from establishing the theory of a divided and definite 
action on the part of each parent, expressly admit the influ- 
ence of both even over the external characteristics. He 
himself says : “ I do not mean it to be inferred that either 
parent gives either set of organs uninfluenced by the other 
parent.” And Dr. Harvey, when speaking of Mr. Orton’s 
strongest instance, the mule and hinny, admits, that “in 
neither hybrid have we the perfect head and limbs of one 
parent grafted, as it were, on the proper body and barrel of 
the other.” The animals are both of them composite ; that is, 
composed, as it were, of both parents, and which it is evident 
would not be the case, provided the male contributed the 
external organs uninfluenced by the female, and the female 
wholly provided the internal organs. This is, in fact, what 
Mr. Orton’s theory would assert, if it could be proved as a 
law liable to no exception. It is so obvious that this is not 
the case, that Mr. Orton himself admits, that there is at least 
one important cause often at work, which is very apt to 
negative entirely his primary law. I shall, perhaps, allude to 
this again before I conclude, as I have to mention other cir- 
cumstances which may often modify or entirely suspend the 
action of this or any other cause that may be named as 
influencing the reproduction of animals. So that, after all, 
we cannot say that we are certain of more than that the 
offspring will exhibit frequently a leaning towards the male 
parent as to external characteristics, and to the female as to 
the internal ones. It is rather singular that this appears 
most strongly in hybrids, which are never likely to become 
general in our principal breeds of domesticated animals, for 
the very existence of these appears to be so opposed to the 1 
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