Cnapter 2 



REPRODUCTION 



Bv George D. Snell, Roscoe B. Jackson Memorial Laboratory. 



The vaginal plug, 55. Gestation, 55. Litter size, 56. Sex ratio, 57. Postnatal 

 development, 58. Ovogenesis, 59. Ovarian regeneration, 64. The estrous cycle, 65. 

 Ovulation, 76. Maturation and fertilization, 77. The transport of sperm and eggs, 

 78. Pseudopregnancy, 78. Corpora lutea, 80. Lactation, 81. Bibliography, 82. 



Since the processes of reproduction are very similar in both mouse and 

 rat, the following discussion includes data from both species. Where no 

 mention is made of the species, it may be assumed that the mouse is the 

 animal referred to. Certain phases of reproduction in the mouse and rat are 

 dealt with much more thoroughly than others. The references listed below 

 contain important material not covered in this chapter. 



Anatomy of the male and female reproductive systems : Chapter 3 of this 

 book. 



Endocrines and reproduction: Parkes (102), Allen (6), Young (137). 



Viabilitv and transport of spermatozoa: Chapter by Hartman, in Allen 



Spermatogenesis : Hays (67) ; see also references in Chapter 3 of this book. 



The vaginal plug. — Copulation in the mouse and rat is accompanied by 

 the formation of the vaginal plug, the presence of which is thus a convenient 

 sign that mating has occurred. The plug is formed by a mixture of the secre- 

 tions of the vesicular glands and the coagulating glands of the male (134, see 

 also p. 137), and in the mouse usually fills the vagina from the cervical canal 

 to the vulva, from which it may even protrude. Occasionally smaller, less 

 conspicuous plugs are formed, a condition particularly common in the case of 

 matings at the first pok partum estrus. Plugs in the mouse usually persist 

 for 18 to 24 hours, occasionally for as long as 48 hours, after which they are 

 sufficiently loosened, probably as the result of leukocytic action, to fall out 

 almost entire (100). 



Gestation. — The gestation period in the non-suckling mouse is usually 

 iQ or 20 days,. (36, 73,. 97, lOoV The frequency distribution of gestation 

 periods of dift"erent lengths for t^yo inbred strains of mice is given in Table i. 



