THE CESTROUS CYCLE IN THE MAMMALIA 61 



The period of gestation in the hedgehog is not more than one 

 month. The Malayan hedgehogs Gymnura and Hylomys are 

 stated to experience an uninterrupted polycestrum. 



In the mole a great development of the male generative 

 organs begins to take place at the end of January, culminating 

 at the end of March. Previous to the end of January it is a 

 matter of great difficulty to distinguish the males from the 

 females without having recourse to dissection. The testicles he 

 on each side of the urinary bladder within the peritoneal cavity. 

 In March they are protruded into sacs, which look hke a con- 

 tinuation of the peritoneal cavity beneath' the base of the tail. 

 Meanwhile the seminiferous tubules within the testicles undergo 

 enlargement, and cells are proliferated, which give origin 

 to the spermatozoa. The prostatic glands, which begin to 

 increase in size in February, acquire enormous dimensions, and 

 conceal the urinary bladder at the end of March ^ {cf. hedgehog, 

 p. 238). At the beginning of the breeding season the male moles 

 fight one another with great ferocity, and one is often killed. 

 Pairing takes place at the end of March, or in April, or some- 

 times as late as early May. A second htter of moles may be 

 born later in the year, but this fact has not been definitely 

 proved.^ 



It would appear that in some Insectivores the prooestrum 

 may be comparatively severe, for in Twpaia javanica Stratz ^ 

 has described a " menstrual " blood-clot which contained pieces 

 of desquamated epithehum. 



Chiroptera 



As will be explained more fully in a future chapter, 

 some species of bats appear to be exceptional in that the 

 season of oestrus does not synchronise with the period of 



' Owen, loc. cit. The same authority states that in the Cape mole (Chryso- 

 cMoris) he found the testes near the kidneys, bat that the vasa deferentia 

 had a oonvolated course, which showed that they underwent periodic 

 movements. Owen also describes the vesiculae seminales in the hedgehog 

 as growing to an enormous size at the season of rut. 



^ Millais, loc. cit. See also Adams, " A Contribution to our Knowledge of 

 the Mole," Manchester Lit. and Phil. Soc. Mem., 1902. 



' Stratz, Dcr gescMeehtsreife Saugethiereierstock, Haag, 1898. 



