ENTOMOLOGY

340 SANITARY ENTOMOLOGYbreeding on the young. This has been observed in the shaft louse ofchickens. On the other hand some of the species, for instance the headlouse of chickens, appear to thrive better on the young than on theadults.Life Hiatoriea.-Very few of the so-called bird lice have been studiedfully. Our lack of knowledge of the life histories and habits of theseparasites is partly due to the difficulty of successfully rearing themunder control. There is a marked difference in the habits of the differentspecies of lice occurring on the same host. This may be explained bythe fact that the parasite has become modified in structure and functionof body parts to live under certain restricted conditions. For instance,on the chicken we find the head louse breeding largely on the head ofchickens and seldom occurring on other parts. This species hangs tothe down on young chickens and is usually found closely adhering to thebase of the feathers on the heads of grown fowls. The body louse on theother hand has adapted itself to living on the skin of the host andis not commonly found on the feathers. This species is very active anddepends for protection on its agility on the comparatively bare parts ofthe skin. The shaft louse usually rests along the shaft of the feathersbut can run freely on the skin, going from one feather to another. Thewing louse is ordinarily found between the barbules on the larger wingand tail feathers, and the fluff louse, a very 'awkward and sluggish species,clings to the fluffy parts of the feathel'S, principally on the thighs andsides.The eggs of the different lice arc laid in the regions where the liceare usually found. The head lice eggs are attached singly to thefeathers on the head and neck. The body lice attach their eggs to thebase of feathers and are usually found in masses, especially on the baseof the feathers below the vent where sometimes the masses become exceedinglylarge-nearly half an inch in diameter.The life histories of a few of the common species have been workedout by Mr. H. P. Wood and the writer. The head louse will serve as anexample. The eggs of this species hatch in from four to five days intominute pale rather active larvae and these after molting their skins severaltime~ become adults in from 17 to 20 days, and egg laying begins afew days later. As far as we have observed, the length of the developmentalperiod of the different species is quite similar.It is difficult to get any ac'curate record of the longevity of lice on thehost but we believe they live for several weeks if not months. When removedfrom the host the longevity is comparatively short and this ofcourse assists in the application of control measures. The body liceusually die within a few hours, while the head and wing lice are morepersistent. Professor Theobald records "keeping the shaft louse alive for