76 Proceedings of the Royal Physical Society. 



As regards the Ceratophylli observed — sciurorum was most probably 

 introduced during the chance visit of an inquisitive Squirrel, though an 

 avian source is not impossible. Or the Squirrel even may have fallen a 

 victim to the Owl. Gallium and fringillce may have come from almost any 

 of the birds noticed. The really surprising feature of the list is its 

 omissions. No mammalian fleas occurred, and the ubiquitous gallimdce 

 failed to put in an appearance. For this reason no effort has been made 

 to identify the castings accurately. Many of the more doubtful feathers 

 have been determined by Mr Eagle Clarke. 



Some additional notes may be given on, 



C. — The Pupal State. 



This may last from a fortnight to several months according to 

 temperature, etc. At the time of writing (31st December 1909), I have by 

 me living cocoons of farreni which were spun not later than the middle 

 of September. Possibly if left alone these would continue unchanged till 

 the return of the Martins in April. Unlike many of our insects which 

 hibernate in cocoons, bird Ceratophylli reach maturity shortly after spinning 

 up. This fact has been noted in many instances (several species) and its 

 occurrence is probably general. If a cocoon be opened, the perfect insect 

 is found already divested of its pupal envelopes. Cocoons may generally 

 be found in deserted nests, among feathers, inside straws, etc., and sometimes 

 form dense felted masses when numerous. They are particularly sensitive 

 to mechanical disturbances. If a small bunch of nest debris containing 

 cocoons be teased out and the mass put in a bag, in a short time all the 

 imagines will emerge. Emergence normally takes place by a forward 

 movement of the insect. It is quickly achieved and jumping may begin 

 at once. Owing to the number of backwardly-directed bristles or spines 

 on these creatures, it is impossible to pull them from the cocoon a posteriori 

 without mutilation. Yet if instead of attempting a forceful eviction one 

 simply stimulates a cocoon behind, the enclosed flea will in the majority 

 of cases come out at once. 



D. — The Imago. 



Adult habits. — At all times Ceratophylli shun light, and in a bag seek 

 the dark corners. When shaken on to a sheet at a window they invariably 

 move towards an observer, which frequently facilitates handling the creatures. 

 Their usual progress is a scrambling run on rough, woolly, or fibrous surfaces, 

 alternating every now and then with apparently aimless leaping. But on 

 smooth surfaces Ceratophylli move almost entirely by leaping. Often when 



