Mammalia: Visceral Systems 61.'» 



agreement in statements of diameters of mammalian eggs as reported 

 by various observers.) Taking it all together, then, it appears that the 

 net reproductive output, measured in terms of number of offspring, is 

 greatest for the smallest mammalian ovaries and least for such gigantic 

 'ovaries as those of large ungulates and whales. 



In most organs there is some functional necessity which requires 

 that the size of the organ shall maintain a certain proportion to that 

 of the animal. The volume of blood varies with the animal's size; 

 therefore the heart and blood-vessels must be of greater capacity in 

 the larger animal. The output of excretory and secretory organs must 

 be proportioned to the size of the animal. In the case of an ovary, the 

 primary and essential function is the formation of eggs. If the pair of 

 tiny ovaries of a mouse can produce eggs in sufficient number to ensure 

 60 or more progeny in a year, why should a whale have about 2 pounds 

 of ovarian substance whose effective contribution to the survival of the 

 species is only a single microscopic ovum in about two years? — "effec- 

 tive" in view of the fact that there is much of what appears to be in- 

 effective activity. In all mammals, so far as is known, a large proportion 

 of ovarian follicles (Fig. 196) suffer degeneration (atresia) before they 

 are fully developed, so that many potential ova never arrive at the 

 possibility of fertilization. 



In the large mammal the multicellular internal structures of the 

 ovary are on approximately the same scale of magnitude as the whole 

 organ. An ovarian follicle in the horse may be a centimeter in diameter, 

 i.e., as large as the entire ovary of a cat. In a whale the larger follicles 

 range from 3.5 to 5.0 cm. in diameter. But the constituent cells of the 

 follicles and of other tissues in the ovary are of the small size character- 

 istic of mammalian cells in general. The size of the egg-cell of placental 

 mammals is consistent with that of tissue-cells, but not with the size of the 

 organ or the animal. 



The minute particle of matter which is potentially a mouse differs 

 visibly in no conspicuous way from the scarcely larger particle which 

 is potentially a 50-foot whale. If it were the business of an ovary 

 somehow to transmit and compress into the egg something representing 

 the whole complex of structural characteristics of the animal to which 

 the ovary belongs (after the manner of Charles Darwin's "pangene" 

 theory of inheritance), it could be imagined that a massive and hercu- 

 lean ovary would be required to pack a whale into an egg no larger than 

 a pin-point. But, in a strict sense, the ovary does not produce eggs. It 

 merely provides a suitable supporting and nutritive substratum for 

 the development of ova whose specific internal structure and poten- 

 tialities have been acquired directly from a preceding egg. A secondary 

 function of ovarian tissue, especially the follicular tissue, is produc- 



