NEMATODE PARASITES OF BIRDS 6 



these hosts are known, and since birds feed to a great extent on these 

 intermediate hosts, the water birds eating entomostracans and the 

 insectivorous birds eating insects, it is not surprising that in birds 

 one finds a great variety of the adult spirurids. The origin of 

 spirurids in birds of prey calls for a different sort of explanation, 

 and a clue to this explanation is afforded in the literature on 

 spirurids. notably in the works of Seurat. Seurat finds that infective 

 third-stage spirurid larvae in arthropods, when eaten by hosts other 

 than the final or primary host, as by rodents, migrate into the tis- 

 sues of such a host and again encyst as third-stage larvae. This 

 has been regarded as a form of aberrant parasitism, but it appears 

 quite likely that this is a customary link in the life cycle of spirurids 

 in birds of prey, the rodent or other host of the encysted third-stage 

 larva serving as a passive vector for the worms. 



In the host list at the end the bird names have been corrected 

 to conform to present-day usage by ornithologists, and the synonyms 

 indicated, whereas throughout the text the hosts are listed as previ- 

 ously reported. 



Class NEMATODA 



Class diagnosis. — Body limited by a cutinous (chitinous) cuticle 

 which may be either plain, striate, or ornamented with markings 

 which may be simple or elaborate. A simple, complete digestive 

 system in typical forms, consisting of a terminal mouth at the an- 

 terior end of the body, followed by an esophagus, and this in turn 

 by an intestine which terminates in an anus in the posterior por- 

 tion of the body. The intestine a tube, rarely with appendages, 

 made up of a single la} r er of cells which face the lumen of the intes- 

 tine on the one side and on the other form the external surface. 

 Body cavity of problematical nature, containing a body fluid which 

 has been the subject of considerable investigation but concerning 

 which opinion varies. Nervous system consisting of a nerve ring 

 .surrounding the esophagus and of nerve cords directly or indirectly 

 connecting with this ring. Muscular system consisting of muscles 

 lining the skin on the inside, excepting on the lateral fields, being 

 arranged longitudinally, the muscles themselves not lined by a lim- 

 iting membrane. Sexes usually separate, though in a number of 

 genera, especially in free-living forms, hermaphroditic, or what 

 Cobb terms syngonic, a condition which perhaps grades into 

 parthenogenesis in some forms. In syngonism the same gonad pro- 

 duces sperm cells and, later, eggs. Genital glands of both sexes con- 

 sisting of tubular structures lying in the body cavity. In the male 

 the genital ducts open to a cloaca. Males usually smaller than 

 females and usually equipped with cutinous (chitinous) copulatory 

 organs known as spicules. Usually one testis in parasitic forms, 



