692 THE MONTHLY BULLETIN. 



may be received because of the progressive diminution in volume. 

 The sound is of a quality to carry well, yet even at very close range it 

 rarely sounds loud. The direction of the performer is usually hard to 

 fix. This shifting, ventriloquistic quality goes well with the shimmering 

 landscape and elusive behavior of the animal, with which it is usually 

 associated in our experience. 



The breeding season begins about the first of March and, in its various 

 phases, lasts ordinarily until the end of May. At the highest altitudes 

 the program is evidently retarded some because of the later advent of 

 warm weather. There is nothing to indicate that more than one litter 

 is produced each year by one female. The instances of late appear- 

 ance of young (for exarhple, in August), where not accounted for by 

 altitude, would seem likely to be due to individual variation in time 

 of development of the reproductive instincts or else to abortion or early 

 death of the first litter. The following is the more or less exact breeding 

 data given in the field notes on file in the Museum of Vertebrate 

 Zoology. 



The earliest date for embryos is February 20 (1910) near Needles 

 on the Colorado River; the number of embryos was eight. On March 

 11 (of the same year), in Chemehuevis Valley, south of Needles, a 

 female was taken containing five embryos. The weather was yet cold, 

 ice on standing water at night. It seems to be a rule with the squirrel 

 family in the desert that the breeding season is so timed that the young 

 of the year are well grown long before the period of intensest summer 

 heat. 



March 11 to 16 (1918) thirty Antelope Squirrels were trapped or 

 shot in the vicinity of Mohave. Of these, seventeen were males and 

 thirteen were females, all adult and in breeding condition. The testes 

 of the males were huge, measuring up to three-fourths of an inch in 

 length. The uteri of the females were heavy- walled, but in only one 

 case were there yet any embryos; one taken March 11 contained five 

 well-developed embryos. The males were lean ; the females all more 

 or less fat. On March 18 (1914) at Victorville two females were taken^ 

 containing thirteen and fourteen embryos, respectively. On March 27 

 (1907), at the same place, a female was found to contain eight embryos. 

 On April 6 (1918), at Olancha, two females contained nine and ten 

 embryos, respectively; and on April 12 one was found to contain seven 

 embryos. On April 24 (1912) at Keeler a female was taken which 

 contained six embryos. 



The average number of young per litter as figured from the above 

 records of embryos is close to nine, with five and fourteen as extremes. 

 Stephens (1906, p. 75) considers five to eight as the usual number. 

 Nelson (1918, p. 443) gives four to twelve. Mearns (1907, p. 301) 

 records that near Mountain Spring, in May, 1894, ten small young of 

 uniform size were caught from one hole. 



The mammfB are generally in five pairs, occasionally in six, rarely 

 five on one side and six on the other. 



The earliest date we have for the appearance of young aboveground 

 is April 23 (1917) at Furnace Creek Ranch, Death Valley; one young- 

 ster scarcely one-fifth grown (its weight was but 17.7 grams) was found 

 wandering about weakly under a mesquite (see fig. 27). The next date 

 is May 13 (1908) for third-grown young at Cabezon, and records for 



