Individual differences : dimorphism : abnormal forms. 



of dimorphism, one instance of which among " anopheles " mosquitoes 

 is well known to us. Major Adie, I.M.S., found that in the Punjab 

 two distinct forms of A. fuliginosus are prevalent during October and 

 November, viz. : the usual form with three white bands on the palpi 

 and three white hind tarsal segments, and a second form with four 

 white palp bands, only two white hind tarsal segments, and slightly 

 different wing markings. It is quite certain that, had specimens 

 of these two mosquitoes been sent to England for identification, 

 they would have been described as distinct species, for Mr. Theobald 

 has founded many of his species upon less marked differences than 

 exist between these two forms. Breeding experiments showed, 

 however, that both forms could be produced from a single pair 

 of parents presenting the characteristic markings of the more 

 usual form, viz., that with three white palp bands and the three 

 terminal hind tarsal segments white. Observations carried on 

 throughout the winter showed that in December and January the 

 usual form was replaced almost entirely by the second form, and 

 that with the onset of spring a return to the ordinary form 

 occurred an excellent instance of seasonal dimorphism. 



Secondly, there is the question of abnormal forms or mon- 

 strosities. During his examination of the types of A. rossi deposited 

 in the British Museum, Mr. Theobald encountered a specimen the 

 abdomen of which was covered with scales arranged as in mosquitoes 

 of the genus Culex. Many thousand specimens of " anopheles " of all 

 kinds had been examined, and this was the only instance in which the 

 abdominal scale structure had resembled that of " culex " mosquitoes. 

 To us it appears very probable that this is an instance of a mon- 

 strosity, and from the remarks in the introduction to his " Revision 

 of the Anophelina " it is evident that Colonel Giles shares the 

 same view. Mr. Theobald, however, classifies the insect without 

 question as the type of a new genus (Aldrichia). Another 

 instance of a monstrosity, which is perhaps even more marked 

 than the above, is the specimen on which Mr. Theobald has 

 founded a new sub-family called Heptaphlebomyina. The single 

 insect, on the characters of which this new sub-family rests, was 

 provided with seven longitudinal veins on its wings instead of 

 only six, as had been the case with every mosquito examined up 

 to that time. 



[6. 



