Fig. 1

Morphological difference of musk glands and testis between the two seasons. a Comparison of muskrat musk secretion weight in the breeding and non-breeding seasons. The left bar represents the total musk secretion weight of 10 muskrats in March and April (17.36 ± 1.67 g). The right bar represents the total musk secretion weight of 10 muskrats in October and November (2.16 ± 0.40 g). The musk secretion weight in the breeding season was obviously greater than that in the non-breeding season (p < 0.01). Different symbols denote statistically significant values (**p < 0.01). b Comparison of testis lengths in the breeding and non-breeding seasons. The left bar represents the average testis length in April (20.6 ± 2.5 mm). The right bar represents the average testis length in November (10.7 ± 1.9 mm). Testis length in the breeding season was significantly greater than in the non-breeding season (p < 0.01). c Comparison of the length of musk glands between the breeding and non-breeding seasons. The left bar represents the average length of the musk gland in April (38.3 ± 4.0 mm). The right bar represents the average length of the musk gland in November (15.3 ± 6.7 mm). The length of the musk gland in the breeding season was significantly greater than that in the non-breeding season (p < 0.01) (**p < 0.01). d Testis morphology in the breeding and non-breeding seasons. e Musk gland morphology in the breeding and non-breeding seasons. f Histological structure of the muskrat testis in the breeding season. g Histological structure of the muskrat testis in the non-breeding season. h Histological structure of the muskrat musk gland in the breeding season. i Histological structure of the muskrat musk gland in the non-breeding season. GC glandular cells, EC epithelial cells, IC interstitial cells, LC Leydig cells, Spg spermatogonium, pSpc primary spermatocyte, rSpd round spermatid, eSpd elongated spermatid