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10 Department of Conservation of Louisiana 



As most of the literature on muskrats states that the 

 young are born "naked, blind and helpless," our field biol- 

 ogist was asked to make a special study of this phase of the 

 muskrat's life history, as it had found that they were not 

 "naked" when very, very young, and during his field in- 

 vestigations Mr. Svihla collected a series of embryos of 

 varying sizes. He reports that "some of the largest had a 

 distinctly sparse covering of their hairs, particularly evi- 

 dent under a low-power lens. The hair covers most of the 

 muskrat with the exception of the top of the head, where 

 internal development is still going on. Evidently this is 

 the last portion to be covered with hair. In still smaller 

 embryos no hair can be seen, but the hair folicles are 

 clearly visible. A very young mouse, evidently recently 

 born, was taken which had a thin covering of hair, even 

 on its head. It was no larger than the largest embryo we 

 have. 



"Further investigation of young mice showed that the 

 sex can be easily told before the guard hairs have developed 

 on the bellies. A fine gray down was found to cover the 

 bellies and the mammae of the females are plainly dis- 

 cernible. By the time the eyes open the fur begins to get 

 darker, larger and thicker, and the mammae are soon 

 covered. 



"During the investigation of the external appearances 

 of the muskrats when young, two cases of females with ten 

 mammae were found — six pectoral and four inguinal." 



It seems very evident that many writers, noting the 

 close relationship between the muskrat and the so-called 

 meadow mouse (Microtus), and, having proved out the 

 period of gestation of the meadow mouse in captivity, 

 blindly accepted the 21-day gestation period, because the 

 muskrat is in reality only a highly specialized enlarged 

 meadow mouse, or vole, as it is sometimes called. 



While we in Louisiana, in spite of our researches, have 

 not as yet proved the gestation period of the Louisiana 

 muskrat, it would appear at this writing that it is longer 

 than 21 days and nearer Mr. Seton's estimate of 30 days. 



