Il6 FLEAS, FLUKES AND CUCKOOS 



and dumpy, whereas the Ceratophyllid fleas are long and loosely built. 

 The resemblance between this species and the common rabbit flea 

 (Plate XI) is also quite obvious, as well as the similarity between the 

 receptaculum of laetitiae and Hoplopsyllus glacialis, the species ofl* the 

 arctic hare (Plate XIII). In the section on evolution we have dis- 

 cussed the origins of the shearwater flea and seen how in the family 

 Pulicidae the change on to a bird host has accelerated the loss of combs, 

 and a shift of the bristles on the tarsi. 



The common rabbit flea congregates on the ears of the host and has 

 become a partially sedentary species. It is attached to the skin of its 

 host by the heavily serrated maxillary lacinia. The shearwater flea has 

 no such modification of the mouth-parts and, as one would expect, is 

 free in the nest and on the host's body. 



Ornithopsylla laetitiae has so far only been recorded in the burrows of 

 the manx shearwater and the puffin, in the Scilly Isles, Skomer and 

 Skokholm Isles, off* the coast of Wales, and Ireland's Eye and the 

 Great Skellig off' the coast of Ireland. The hosts occasionally nest on 

 the mainland but so far the flea has not been found anywhere except in 

 tliese remote islands. The puffin is a popular bird with fleas, six species 

 having been recorded from it, namely: C. gallinae, C.garei, C. vagabunda, 

 C. borealisj 0, laetitiae and the common rabbit flea Spilopsyllus cuniculi. 

 The shearwater on the other hand has one flea only, 0. laetitiae, and it 

 is probably its true host. 



Conclusion 



Bird fleas are a small group and their chief interest lies in the fact 

 that they have transferred from mammalian to avian hosts in compara- 

 tively recent times. Thus, the evolutionary trends associated with the 

 change to life in feathers are relatively easy to observe and a gigantic 

 and instructive field experiment is presented to the naturalist should he 

 care to avail himself of the opportunity of studying it. The cardinal 

 need, in the first place, is further collecting. And again further collect- 

 ing. The first line on which to concentrate is the fleas from ground- 

 nesting birds, particularly from those species which nest in isolated 

 island habitats, in holes and caves. The student of bird fleas who 

 reads Murphy's Oceanic Birds of South America almost expires with 



