so THE PHYSIOLOGY OF REPRODUCTION 



at least, as a compensation for the amount of blood lost." These 

 results should be compared with those recorded for menstruating 

 women (see p. 63 ; also p. 391 and Chapter XI.). 



The histological changes which take place in the uterus during 

 the oestrous cycle are described in the next chapter. 



The period of gestation in the dog varies from fifty-nine to sixty- 

 three days. With dogs belonging to the smaller breeds the period 

 is often somewhat less than with large dogs. The period of lactation 

 is very variable in duration, and may extend until the commencement 

 of the next prooestrum. Pseudo-pregnancy may occur in the dog. 



The wild dog of South America (Canis azarce), according to 

 Rengger,! breeds only in winter, and therefore but once a year. 

 The same is said to be the case with the wolf ^ and the fox in their 

 wild state ; but these animals, in the Zoological Gardens in London, 

 experience two annual " heat " periods like the dog.^ The wolves 

 in the Dublin Gardens, however, are stated to have only one annual 

 sexual season when permitted to breed; otherwise they come "in 

 heat " more frequently, but are always monoestrous.* The period of 

 gestation in the wolf and fox is approximately the same as in the 

 dog, i.e. about two calendar months. 



Bischoff^ refers to the fact that the sexual season of the fox is 

 affected by the nature of the country which it inhabits, foxes which 

 live at high altitudes breeding later than those residing on the 

 plains. Millais" says that fox-cubs in most parts of Britain are 

 not born until the end of March or beginning of April, whereas, 

 in the South of England, they are often produced as early as 

 January. 



The Cape hunting-dog {Lycaon pictus) has been known to have 

 bred in captivity on several occasions, and notably in the Gardens 

 at Dublin, where six litters were produced from a single pair between 

 January 1896 and January 1900. The first three litters were born 

 in January, the fourth in November 1898, the fifth in May 1899, 

 and the sixth in January 1900. Cunningham writes : " It is not 

 easy to offer a satisfactory explanation of the irregularity of the 

 fourth and fi'fth litters. I am inclined to believe, however, in the 

 absence of definite information on this point obtained from the animals 



^ Rengger, Natxirgeschichte d. Saugethiere von Paraguay, Basel, 1830. 



2 John Hunter {Animal (Economy, London, 1786) says wolves breed in 

 December. 



^ Heape, loc. cit. 



' For the information regarding the breeding of the animals in the Royal 

 Zoological Society's Gardens, Dublin, I am indebted to the late Professor D. J. 

 Cunningham and Dr. E. F. Scharf. (See Marshall and Jolly, loc. cit.) 



5 Bisetfoff, "Ueber die Eauhzeit des Fuchses und die erste Entwicklung 

 seines Eies," Sitz. der Math.-phys., Wien, Classe vom 13 Juni, vol. ii., 1863. 



'' Millais, loc. cit. 



