THE CESTROtrS CYCLE IN THE MAMMALIA 55 



Thus the nursing or lactation period extends for nearly two years, 

 while gestation lasts about one year.^ 



Insectivoea 



The majority of the animals in this order are almost certainly 

 polyoestrous, but comparatively little is known concerning their 

 breeding habits. The shrew in this country may be found breeding 

 in any month from April until November, so that it is practically 

 certain that this animal is polycBstrous, and may have two litters, if 

 not three litters, in a year. It is extremely probable also that the 

 water-shrew breeds twice a year. In the litedgehog, in this country, 

 litters are born at the end of May or June, and in August or 

 September.^ In Germany it is said that the breeding season extends 

 from March until July.* The period of gestation in the hedgehog is 

 not more than one month. The Malayan hedgehogs Cfy^nnura 

 and Hylomys are stated to experience an uninterrupted polyoestrum. 



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 lie on each side of the 

 urinary bladder within the peritoneal cavity. In March they are 

 protruded into sacs, which look like a continuation of the peritoneal 

 cavity' beneath the base of the tail. According to Regaud and 

 Ldcaillon they increase in size sixty-four times.* 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 ^ (of. hedgehog, p. 250). 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 



' Millais, loc. cit. 



''■ Millais, The Mammals of Great Britain and Ireland, vol. i., London, 1904. 



^ "Van Herwerden, "Beitrag zur Kenntniss des mehstruellen Cyklus," 

 Monatsschr. f. QeburtshiUfe und Gyndlc., vol. xxiv., 1906. For further informa- 

 tion see Marshall, "The Male Generative Cycle in the Hedgehog," Jour, of 

 Physiol., vol. xliii., 1911 ; and Tandler and Gross, Arch. f. Entwick. Mech., 

 vol. xxxiii., 1911. 



* Adam^, " Sexual Life of Mole," Jour. Ministry of Agric, vol. xxxvii., 1920. 

 Kegaud, "Btat des Cellules Interstialles chez la Taupe," C.R. de U Assoc. Anat., 

 Suppl., 1904. Ldcaillon, "Sur les Cellules Interstialles du Testicule de la 

 Taupe," C.R. de la Soc. de Biol., vol. Ixvi., 1909. 



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

 chloris) he found the testes near the kidneys, but that the vasa deferentia had 

 a convoluted course, which showed that they underwent periodic movements. 

 Owen also describes the vesiculse seminales in the hedgehog as growing to an 

 enormous size at the season of rut. 



