234 OSCAR RIDDLE 



is divided into its natural divisions; i.e., into the actual periods of 

 work and rest of the female parent. It will be observed that both 

 females threw highest proportions of male offspring from the 

 longest clutch intervals and fewest from the shortest intervals. 

 In the eight instances there is not an exception. Moreover, 

 when each of these natural periods is subdivided into a first and 

 last half and the clutch intervals and the sex ratios are calculated 

 anew (columns 2 and 4, tables 3 and 4), the same fact is again 

 demonstrated. Wlien the undivided natural periods are put 

 alongside the sex ratios, calculated as percentages, the figures 

 speak for themselves : 



9 A248 9 60 



16.5da.= 26^: 1 9 = 33 . 3% females 14.5 da. = 12 c? : 10 9 = 45.5% females 



7.6 da. = 16c? : 10 9 = 38.5% females 9.9 da. = 10c? : 10 9 = 50 . 0% females 



7.4da. = 17c? :179 =50.0%females 7.7da. = 6c? : 15 9 = 71. 4% females 



7.0da. = 4c? : 16 9 =80.0% females 7.1da.= 4c? : fl 9 = 73.3% females 



Twin from six-day interval Twin from seven-day interval 



In this connection we may consider the question whether the 

 parents continued to produce eggs immediately after the twin- 

 producing eggs were laid and what was demonstrated as to the 

 sex ratios in these eggs. Reference to table 2 will show that the 

 hybrid female (60) laid only one other clutch of eggs before taking 

 a rest (forty-four days). We are therefore unable to say what 

 the sex ratio from this female would have been had she continued 

 'crowded reproduction.' The period of rest is, of itself, however, 

 an evidence of the w^eakness (following overwork) which we have 

 learned to associate with a high proportion of females. But even 

 the next complete reproductive period following this period of 

 rest yielded eleven females to four males, with two additional 

 embryos too weak to hatch. In the case of the other twin- 

 producing parent ( 9 A248, table 1) it will be observed that egg 

 laying was continued at regular seven-day intervals for twelve 

 clutches after the twin-bearing clutch. From these eggs four 

 males and sixteen females were produced, and four eggs were too 

 weak in developmental power to permit us to know their pros- 

 pective sex. Here one series of eight consecutive eggs produced 

 females; another unbroken series of five eggs produced females. 



