WORMS 197 



common snipe in Britain. Other species of the genus are found in gulls 

 and A. dujardini is a parasite of starUngs and thrushes. 



A species of the genus Tetrabothrius is found in the eider duck, but 

 not in the domestic duck. This genus, which is a north European, 

 North American and Arctic group, is chiefly characteristic of sea birds, 

 such as the gulls and terns, but is also found in whales. In Britain 

 T, cylindraceus has been recorded from the manx shearwater, herring- 

 gull and fulmar, and T. macrocephalus from the red-throated diver, black- 

 throated diver and great crested grebe. One specimen of T. erostris was 

 collected from the glaucous gull. 



An important family is the Davaineidae, which includes the large 

 genus Raillietina. These tapeworms are chiefly characteristic of the 

 orders Galliformes (gamebirds) and Golumbiformes (pigeons) although 

 several species, such as R. anatina, have been recorded from the duck, but 

 not yet from Britain. The known intermediate hosts include ants, flies, 

 beetles and snails. The same remarks apply to the allied genus Cotugnia. 



Recently a great deal of attention has been centred on cestodes of 

 the family Anoplocephalidae, which are common parasites of mammal- 

 ian herbivores. One of the great mysteries of helminthology was solved 

 when Stunkard proved that the intermediate hosts of Moniezia are 

 oribatid mites, many of which live near the roots of the grass and are 

 accidentally ingested by the host while it is grazing. It will probably 

 be found that Aporina delafondi, which is a widely distributed parasite 

 of pigeons and turtle-doves in the Old World , has a similar life- 

 cycle. 



Large numbers of hyper-parasites have been recorded from worms. 

 A book of over 450 pages has recently been published, compiled by 

 Dollfus, dealing exclusively with the parasites of helminths. Protozoa, 

 bacteria, fungi and other worms are the principal enemies. Generally 

 these organisms are mentioned in passing by the authors who are more 

 interested in the worms themselves. Birds must also rank as enemies, for 

 they search systematically for ripe proglottids containing eggs in the 

 faeces of animals and eat them with enthusiasm. We have already 

 mentioned that, at times, the sheath-bill {Chionis alba) subsists largely 

 upon the parasitic worms it finds in the faeces of colonial nesting birds, 

 particularly the gentoo penguins. As tapeworms require an inter- 

 mediate host for development the sheath-bills do not themselves 

 become infected, although they are continually ingesting millions of 

 ripe eggs. 



