24 



The Philippine Journal of Science 



1918 



known to have taken blood is little greater than that of those 

 exposed two or three times without segregation of those known 

 to have taken blood. 



The explanation of the great variability in the infectivity of 

 gamete carriers independently of the percentage of gametes in 

 the blood is not apparent. Dr. S. T. Darling has suggested that 

 it is due to a disparity in numbers of the sexes of gametes. It 

 may be also conceived that in the presence of a sufficient number 

 of both sexes there is in gametes some biological factor, not 

 apparent morphologically, which determines their fertility. 

 Possibly gametes originating in the same oocysts, or it may 

 be in the same mid-gut, are less mutually fertile than gametes 

 from more widely differing sources. Analogies will be found 

 in other organisms. Further data will be necessary for the 

 explanation of this problem. 



In Table X may be noted the failure of umbrosus collected in 

 the imago stage to become infected. Further data on the relation 

 of the source of mosquitoes to their susceptibility to experimental 

 infection with malarial parasites are included in Table XII, 

 where the percentages infected and the average number of 

 oocysts per infected gut are compared with respect to the source 

 of the insects "used. Only controlled series and only the four 

 species of which material was taken in the adult stage are in- 

 cluded in the table. 



Table XII. — Certain species compared as to the susceptibility of material 



from different sources. 



Species of Anopheles. 



Mosquitoes collected in 

 imago stage. 



Mosquitoes collected as 

 larvae or pupse. 



Dis- 

 sected. 



Positive. 



Average 

 oocysts. 



Dis- 

 sected. 



Positive. 



Average 



oocysts. 



A. umbrosus 



100 



12 



2 



15 



Per cent. 

 6.0 



8.3 



0.0 



26.7 



4.5 



8.0 



0.0 



«16.5 



43 



117 



67 



5 



Per cent. 

 44.2 



15.6 

 62.7 

 100.0 



3.3 



12.3 



19.0 



a 82. 2 



A. rossi var. indefinitus, brackish 







Total 





129 



8.5 



9.2 



232 



41.4 



14.5 





Entry recorded as "very many." Here reckoned as 50 oocysts. 



It is seen in Table XII that mosquitoes collected in the adult 

 stage show in every species a lower percentage of infection, and in 

 the total and every species but one a lower average number of 

 oocysts per infected gut than mosquitoes collected as larvae or 



