SECOND AXNUAL MEETING 67 



fore the birds are cookefl, hut also that the species of Entozoa which 

 are at home in l)ircls are not such as attack man; and should one come 

 bj' chance into the human alimentary canal, it would not be able to 

 maintain its position there. At least in all the recorded observations 

 on human parasites, which have been more carefully studied than those 

 of any other host, there is no mention of the occurrence of an avian 

 form. On the other hand the influence of the parasite on the host is 

 of importance. Birds are, comparatively speaking, badly infested with 

 parasites, and in proportion to the volume of the host the parasites are 

 proportionately large so that their effect must be all the more notice- 

 able. The draft on the host for nourishment, the Irritating effect of the 

 parasite in the alimentary wall, and the tendency to occlude the canal 

 are all factors which must be considered. But the most unfortunate 

 fact in the presence of parasites is the possibility of an epidemic which 

 is given thereby. 



It is a characteristic feature of Entozoa that the reproductive jjower 

 is greatly above that of free-living species in view of the conditions 

 which ordinarily combine to destroj' the larva before it can reach a new 

 host. Under usual circumstances, then, only a small fraction of the 

 embryos develop to mature individuals. There arise, however, from time 

 to time such conditions as bring to maturity an unusual number of 

 l^arasites. What siich conditions are cannot be stated in general, for it 

 depends upon the life historj- of each particular species. It may be 

 that a wet year, the abundance of some other form of animal in which 

 one stage of the life history is passed, a mild winter, or even more 

 trivial factors bring about unexpectedly- a radical increase in the num- 

 bers of a certain parasite, and there results in consequence a parasitic 

 epidemic v^^th serious results to birds of a given species and territory. 

 Such eiiidemics, due to cestodes and to trematodes, are recorded in 

 Europe among game birds and no doubt are more frequent than is 

 evinced bj- the records. 



In view of these facts it is important to secure more extended infor- 

 mation regarding the degree of infection to which American birds are 

 subject and the species of parasites by which they are infested. During 

 the past eight years the Department of Zoology at the University of 

 Nebraska has been collecting material and keejiing very precise records 

 of these facts for such Nebraska birds as could be examined. There 

 are included in the hosts examined both native and migratory birds, 

 and the records have been made by a considerable number of observers 

 to all of whom I am much indebted for the assistance given thus. 



Considering first the question of the species of parasites found, one 

 may say that the statement of Cobbokl (69) regarding the parasites 

 of English birds is equally true of these from Nebraska birds; they 

 cannot yet be satisfactorily defined or identified. It will be the work 

 of some time to determine clearly how many are new^ and how raany 



