CYCLIC CHANGES IN UTERUS AND OVARIES. 33 



some will be seen sitting quietly, some eating a little, or walking 

 about, making a small, sociable clucking noise. 



"If one moves occasionally, rather majestically, among the 

 rest, making a low, purring noise, similar to the noise of the male, 

 she is probably in heat; if not, she soon will be. In some cases, 

 a female guinea-pig may reach a state of excitement in which 

 she assumes the manners of a male and attempts copulation 

 with another guinea-pig which happens to be in heat. She, 

 as well as the second guinea-pig that allows her to attempt the 

 role of a male, will almost always be found ready for copu- 

 lation. 



"In many other cases, however, no such clear indications are 

 present, but on close observation it will be seen that some female 

 which is sitting quietly will be found to elevate slightly her hips 

 whenever another guinea-pig happens to touch her. Again 

 other females will show no sign of their condition, unless an 

 active male is put among them. Those in heat take interest in 

 the male, when he comes near them, while those not in heat or 

 near the period of heat will kick him and hop away, making a 

 little complaining noise when he pays attention to them. The 

 male has no means of selecting the females which are in heat. 

 When he has accidentally found one, he cannot find her again 

 a moment later, but must try every female which he happens to 

 come near to until he by chance meets again the animal in heat. 

 Neither do the females that are in heat go to the male, but they 

 wait, wherever they happen to be, until he comes to them. 

 Some females will not give any indications whatever of their 

 condition, but only when the male attempts copulation will 

 they be found to be in heat. 



'There are occasionally individuals which always appear to 

 be in heat; at frequent intervals when not busy eating they purr 

 and walk about like a male, but never seem to be actually ready 

 for copulation. They resent the advances of the male at all 

 times and yet are not sterile; when left for some months in a 

 lot of males and females they may become pregnant. 



'When one or very few females are kept in a small cage and 

 have become relatively tame, those in heat when tickled along 

 flanks and hips will react to the touch of the fingers, assuming a 



