90 BULLETIN 903, IT. S. DEPARTMENT OF AGRICULTURE. 



rect and that the disproportionate mortality among the eggs was 

 caused rather by the uneven temperatures prevailing in the room. 

 The presence or absence of humidity had no apparent effect on the 

 deposition of eggs. Eggs and sexed forms developed better in dry 

 than in moist rubber cells, but in the dishes exposed to light the 

 converse occurred. Part of the migrants were stimulated to fly in 

 the sunshine before being placed in the cages, and deposited a some- 

 what larger average number of eggs than those which had not flown, 

 but the flight or nonflight of the migrants did not appear to influ- 

 ence the subsequent development of the eggs and sexes. In July 

 and the first half of August, when the temperatures reached a maxi- 

 mum, there was a higher average in egg production and in the pro- 

 portion of sexuals matured, yet during the period September 16 to 

 October 27, despite lower temperatures, a larger average proportion 

 of eggs per migrant and of mature sexes was produced than during 

 the intermediate period from August 16 to September 15. 



On the whole, development was most successful where migrants had 

 flown and when eggs were kept in moderate light and in a moderately 

 humid environment. 



The longevity of the migrants, the number of eggs deposited per 

 individual, and the proportion of male and female eggs laid coin- 

 cided with the results of experiments in 1914. 



It is only necessary to consider the very small proportion of eggs 

 laid per migrant (in 1915, for instance, 1 to 4.15) and the very 

 .small proportion of eggs which succeeded in developing into mature 

 sexes (in 1915, 1 in every 9) under artificial conditions to realize 

 how abnormal these conditions must have been. From observa- 

 tions made in California during 1915 the complement of migrant 

 eggs was found to average 2.6, so that if all the migrants in the 

 experiments in that year had deposited their full complement, ten 

 times as many eggs as were actually deposited would have been 

 obtained. European experimenters have had, for the most part, 

 similar results in their study of migrants in confinement. 



In not a single instance was a migrant observed to deposit other 

 than a sexual egg, so the possibility of the occurrence in California 

 of a parthenoparous winged form may be regarded as excluded. 

 There occurs, however, a parthenoparous nymphical form, which has 

 been discussed above (p. 82). 



THE SEXUAL FORMS. 



The sexual forms (PI. VIII, j-ni), male and female, issue from 

 eggs deposited by the winged sexuparse or migrants. These eggs 

 are of two types,' male (PI. VIII, /) and female (PL VIII, A, i). 

 Writers have attempted to recognize a third type intermediate in size 



