292 THE POPULAR SCIENCE MONTHLY 
THE PALEONTOLOGIC RECORD 
ONTOGENY: A STUDY OF THE VALUE OF YOUNG FEA- 
TURES IN DETERMINING PHYLOGENY 
By Prorrssor F. B. LOOMIS 
AMHERST COLLEGE 
ae this paper I want to study what value is to be given to the prin- 
ciple that ontogeny is a brief recapitulation of phylogeny, when it 
comes to the concrete determination of the ancestry of a given genus. 
For the purpose three types have been studied carefully and several 
more for confirmations, the principal study being between the young 
and adult of the pig, cat and man, the differences being noted to see if 
they suggested the forms considered ancestral. 
First let us consider the skull of a six weeks’ pig in comparison with 
that of the adult, the two having been drawn to the same length. The 
first and most marked variation is in the brain case, that of the young 
being relatively vastly larger. The same is especially true of the sense 
capsules of the ear and eye. The later growth is much greater in those 
parts of the skull designated as facial, or having to do with the jaws and 
their supports. Then there is a change in the axis of the skull, this 
being due to the growth of the maxilla region, and lastly where there 
is any cellular bone or bone spaces they are developed in later life. 
This factor is especially well shown in the development of the elephant 
skull] and in ruminants. It is coincident with high crests and marked 
protuberances. 
While most of the features have been indicated in the pig, the same 
comparison in the cat reveals the same excessive development of the 
brain case and sense organs, the same weakness of the jaws and change 
in the axial relations, and this may be further confirmed in looking at 
the contrast between a three-year-old child’s skull and that of an adult. 
The conclusions then to be drawn from this hasty comparison of 
the two skulls are, first, that the shape of the skull in the young shows 
the excessive development of the brain and sense capsules, so that the 
appearance is not that of a primitive animal, but exactly the contrary, 
the appearance which the genus would assume were its mental or 
nervous development carried to a much higher degree than is the case. 
The embryonic development of the brain and sense organs is pushed 
far toward the beginning, and is matured, as far as size is concerned, 
the earliest of any of the systems. ‘The skull is first an envelope for 
the brain and sense organs and is therefore profoundly modified by this 
embryonic peculiarity, and the younger the individual the less like the 
adult or ancestor the skull is shaped. 
