314 KELLOGG AND BELL 



and necessarily much in-and-in breeding. It is a condition 

 analogous to island life carried to an extreme of isolation of 

 small groups of individuals of the same species. The meta- 

 morphosis of the Mallophaga is incomplete. 



On the latero-posterior angles of the dorsum of the metathorax 

 of all species of the genus Lipeurus, parasitic on birds, are 

 certain very long, spine-like hairs (fig. 80), probably tactile in 

 function, whose number and arrangement vary in different 

 species, but are presumably constant for any given species. 

 The number of these hairs is used to some extent in distinguish- 



FIG. 80. The biting bird louse, Lipeurus celer, and diagram of metathorax 

 (enlarged) showing tactile hairs in lateral posterior angles. 



ing species of the genus. We have examined the variation in 

 number of these hairs in 239 individuals of JLipeurus celer 

 Kell., a parasite of the fulmars, Fulmarus glacialis vars. 

 rodgersi and glupisckka. These individuals were taken from 

 31 Fulmarus glacialis hosts, shot in the Bay of Monterey, 

 California, in a time period of two weeks. 



The range in number of the tactile hairs is from 3 to 6, with 

 4 as the mode, the mode occurring in a large majority of cases. 



