Mammals 37 



relative lengths of the large and small intestine were charac- 

 teristic of genera and species, and yet showed extraordinary 

 variation. Inasmuch as the intestines are constantly in use, one 

 might suppose that natural selection would have kept those of 

 each species near to an optimum length, whatever that might be. 

 Instead of that, there is probably no part of the body, unless it 

 may be the liver, which shows so much variation. It appears 

 that some portions of the soft anatomy are not as essential as 

 might be imagined, and that there may be superfluous lengths of 

 intestine, serving no important purpose. My former teacher, 

 Sir John Bland-Sutton, has just published a paper in which he 

 shows that the human gall-bladder, if diseased, may be safely 

 removed.* 



In the gopher Cratogeomys castanops we were surprised to 

 find that the large intestine is longer than the small; the large 

 varying from 48.3 to 61 cm. the small 34.3 to 47 cm. Subsequent 

 studies by Miller and Printz, not published, showed that the same 

 thing is true of the vole Microtus mordax from Eldora. The large 

 intestine in this animal varied from 51.5 to 58 cm., the small from 

 41.8 to 46 cm. The ratio of five specimens, taking the small 

 intestine as 100, was 122:100, 123:100, 123:100, 123:100, 130:100. 

 We were curious to know whether this condition obtained in 

 other species of Microtus, and Mr. H. E. Anthony was so kind as 

 to measure some specimens (in alcohol) of M. pennsylvanicus, 

 with the following result: large intestine 29.5 to 37 cm. small 27 

 to 37.5 cm. Of the three specimens examined, two had the 

 large intestine longest; but the third, an adult female, had the 

 large 37 cm., and the small a trifle longer, 37.5 cm. It will be 

 seen that in spite of the great variation, these figures are in com- 

 plete contrast with those obtained from many other rodents, 

 such for instance as the house mouse and the Norway rat. In 

 the house mouse the usual measurements are about 9 cm. for the 

 large intestine and 40 for the small. In the Norway rat the large 

 intestine is from 10 to 18% of the small. Intermediate ratios 

 are found in the white-footed mice; thus Peromyscus maniculatus 

 rufinus had the large intestine 37 to 57% of the small. A white- 



*British Medical Journal, Nov. I, 1924. "The mere loss of the gall-bladder is unattended 

 with sinister consequences. Many mammals and birds lack a gall-bladder. Some parrots 

 have a gall-bladder and some not. Absence of the gall-bladder neither causes inconvenience 

 nor shortens life." 



