Some Habits and Hosts of Bird Ceratophylli. 79 



hinged lobes, enters the duct a distance of - 3 m. — - 4 m. (farreni). Its entrance 

 is facilitated probably by the displacement of a small chitinous structure 

 lying at the mouth of the duct. The terminal triangular lobes, referred to 

 above, from lying in a straight line with the internal penis, move down- 

 wards through a right angle. Their effect in tightening the membrane 

 (9th tergite $ ?) on which they press, can plainly be discerned. Their 

 points also compress the rectum of the % behind the 10th sternite. 



Speaking generally one would say that this complex arrangement of 

 parts is a lock and key to prevent crossing with another species. It is not 

 so easy, however, to explain details. Clearly the great reduction of the 

 8th sternite $ is correlated with the position assumed in copulation. If 

 the $ 8th sternite were like that of the $ it would be impossible for him 

 to bend under her as he does. By impinging on the pygidium of the $ 

 the bristles of the 8th sternite $ may supply some necessary stimulus. 

 It is noteworthy that three parts of the $ appendages converge on or near 

 the 10th $ segment. This may be either to hold the £ securely or to close 

 the anus. Both interpretations may be correct, and certainly the second 

 is suggested by the presence of the hairy flaps (rising at the basal ventral 

 angle of the 9 th sternite $ ) behind the $ anus. 



Several trials showed that copulation is the first business of the imaginal 

 state. It proved much easier to induce this condition than to fix the 

 insects in position. Dropped into alcohol (70 °/ o ) they struggled apart 

 long before death. A mixture of absolute alcohol, chloroform, and glacial 

 acetic acid, in equal proportions, was hardly more effective. Suddenly 

 treated with chloroform or ether, the relaxation of the insects was so great 

 that they fell apart. By gradual narcotising and subsequent plunging into 

 a quick fixative one or two pairs were secured without much alteration. 

 Boiling water also in one case proved a satisfactory killing agent, and 

 decapitation with a sharp razor was sometimes successfully tried. 



Summary. — Bird fleas breed in the nests of their hosts either by the 

 carrying there of pregnant £ $ , or by the rarer introduction of eggs shaken 

 from the birds' plumage. After a life-history [i.e., from hatching of 

 the ova to emergence from the pupse) of about a month new imagines 

 are born and copulate at once. Successive broods will be produced so 

 long as the conditions of food, temperature, etc., are favourable. If the 

 numbers born are large, an exodus may occur. Of the last brood many 

 probably wait the return of spring before hatching out, but there is 

 evidence to show that any casual visitor to a deserted nest in winter 

 may carry away fleas. 



The whole subject of this life-history, however, bristles with difficulties 



