348 



THE AMERICAN NATURALIST 



[Vol. LVI 



siderable importance that they be fed with the greatest 

 regularity. 



Several animals were lost during the course of the ex- 

 periments and in each case a necropsy was performed. 

 Illness, in several of the animals, extended over a period 

 of weeks. They lost steadily in weight, and tended to 

 assume a characteristically crouching attitude. The fur 

 became rough and tousled. Some of them chewed in- 

 cessantly, although some pain seemed to be associated 

 with the process. The full significance of this behavior 

 was made clear at the necropsy. Guinea pig No. 7, for 

 example, which succumbed after an illness of three weeks, 

 had an empty stomach, and the abdominal cavity was 

 absolutely devoid of fat. There were no macroscopic 

 signs of infection or disease. E^jamination of the teeth 

 revealed that the upper incisors were worn down almost 

 to the gums, with a more than corresponding increase in 

 the length of the lower incisors, making occlusion of the 

 molars impossible. The molars were loose and could 

 easily be picked from the jaw with an ordinary labora- 

 tory forceps. 



The body of guinea pig No. 12, which died with prac- 

 tically the same symptoms, showed extreme atrophy and 

 emaciation. Ascaroid parasites were found in the rectum. 

 The upper incisors were loose and worn and the short 

 stumps remaining could be be removed with the fingers. 

 The upper and lower incisors were separated by about 8 

 mm., due to the fact that the molars occluded first and pre- 

 vented the short, probably fractured incisors from meet- 

 ing. From the findings in these cases it would seem that 

 guinea pigs may die of starvation because of the presence 

 of worn or irregular teeth and consequent inability to 

 masticate food. It may perhaps be that the changes in 

 the teeth of these animals were due to senility, but fur- 

 ther observations are necessary to confirm this before a 

 definite answer can be given to the question. 



In order to study daily stages in the pregnancy of guin- 

 ea pigs it became necessary to mate a large number of 

 animals and to know the exact time of copulation. Stock- 

 ard and Papanicolaou, '17, studied the oestrous rhythm of 



