326 Department of Conservation of Louisiana 



cement-lined enclosure to allow some greens to grow so as 

 to vary the monotony of the diet of rolled oats, apples, 

 turnips, etc., fed the animals and a good-sized bathing pool 

 should be a part of the equipment. If space permits, a 

 series of such pens can be constructed, but emphasis must 

 be placed on the cost of such equipment, a cost that will 

 not be refunded if the animals are raised solely on a pelting 

 basis. 



By this "complete control" method data can be kept on 

 breeding habits and, perhaps, the knotty problem of the 

 period of gestation can be untied. As has already been 

 stated, it has not been conclusively proved that the period 

 of gestation of the muskrat in all sections of its range on 

 this North American continent is exactly 21 days, nor do 

 we know to a certainty just how many litters can be pro- 

 duced in the period of a twelve-month. 



Dr. Johnson, in his "The Muskrat in New York" says 

 that the exact period of gestation of the muskrat has not, 

 so far as he is aware, ever been determined and points out 

 that some investigators, on the basis of analogy with the 

 common house rat, have suggested that the period of gesta- 

 tion is not more than 21 days. 



That distinguished writer, artist and naturalist, Ernest 

 Thompson Seton, gives the period of gestation as "probably 

 30 days" and our experiments and surveys in Louisiana 

 seem to bear out Seton's figures, although we have arrived 

 at nothing definite or concrete on this moot question. 



The most reliable data as to the number of young pro- 

 duced in a litter are furnished by records of embryos con- 

 tained in the uterine horns. Such records gathered by the 

 Biological Survey naturalists and others indicate a wide 

 variation, i. e., Seton gives the muskrat from 4 to 9 in a 

 litter; Biological Survey data show 3, 6, 8, and even 13 

 fetuses found in different females. Dr. Vernon Bailey's 

 observations in Montana heading the list with 13 found in 

 one female, June 18, 1895. In the Imperial Valley, South- 

 ern California, where muskrats have been introducted in a 

 desert turned into an Eden by artificial irrigation, Dr. Jo- 



