208 ROYAL NORTON CHAPMAN 
but in such cases some other means of support for the viscera 
have been supplied. 
This series of structural modifications so well correlated with 
the habits of the animals may justify one or more of the following 
conclusions: (1) that the correlation is a coincidence due to chance 
and that by the same chance other types of pelvis do not exist 
among the forms studied; (2) that from a number of chance varia- 
tions in each group of burrowing mammals, the most efficient 
burrowing structure has been preserved by natural selection; 
(3) that similar forces acting in a similar way have been factors 
in causing similar modifications of structure in animals belonging 
to widely different systematic groups, just as tuberosities develop 
on bones at the points of attachment of muscles of strenuous 
action. A combination of the second and third conclusions seems 
to be in entire harmony with the findings in this study and 
ascribes a dominant influence to the environment in the produc- 
tion of the parallelisms in the forms studied. 
LITERATURE CITED 
Broek, A. J. P. v. d. 1914 Studien zur Morphologie des Primatenbeckers 
Morphologisches Jahrbuch. 1914-15; Bd. 49; ppl-118. 
Dosson, C. E. 1882 A monograph of the Insectivo_a, systematic and ana- 
tomical. Par. I. London, 1892. 
Huxuey, Tuomas Henry 1875 On the characters of the pelvis in the Mam- 
malia, and the conclusions respecting the origin of the Mammalia 
which may be based on them. Proceedings of the Royal Society of 
London, 1878-79, pp. 395-405. 
Lecxre, W. 1884 Mammalia, pelvis. Bronn, Klassen und Ordnung des Tier- 
reichs. 1892, Bd. 6, s. 571. 
1892 Mammalia, Myology. Bronn, Klassen und Ordnung des Tier- 
reichs, Bd. 6, s. 784. 
OsporNn, Henry L. 1894 Notes on Geomys bursarius. Science, vol. 23, p. 102. 
Seton, Ernest THompson 1909 Life; Histories of northern animals. New 
York, 2 vols. 
Suinner, H.W. 1903 Adaptations to aquatic, arboreal, fossorial, and cursorial 
habits in mammals. III. Fossorial adaptations. American Natural- 
ist, vol. 37, pp. 819-825. 
SHutu, A. FRANKLIN 1907 Habits of the short-tailed shrew, (Blarina brevi- 
cauda). American Naturalist, vol. 41, pp. 495-522. 
Tuomas, P. 1885 Proceedings of the Zoological Society of London, 1885,,p. 611. 
Drawings by Helen Sanborn Chapman, Department of Animal oleae The 
University of Minnesota. 
