CARCINOMA OF THE THYROID IN SALMONOID FISHES. 501 



as A . duodenale with reference to dogs, are sufficient to indicate that stray parasites may enter the body 

 through the skin as well as through the mouth, and perform extensive migrations through the tissues 

 and even undergo a partial development before they die. The possibilities as to the amount of damage 

 such stray parasites may do are interesting. They may, for instance, have more injurious effects on 

 the unusual host than on the animal to which they are specifically adapted, much as in the case of 

 various parasitic protozoa which do not injure certain animals considered to be their usual hosts, but 

 are very injurious to others considered unusual hosts. The two cases are of course not strictly com- 

 parable as there would be no multiplication, at least no repeated multiplication, in the case of the 

 nematode like that in the case of the protozoan. The introduction of microorganisms by nematode 

 larvae is another possible source of damage, and this applies not only in the case of stray parasites but 

 in the case of those entering their proper host animals. Many parasitic nematodes have plenty of 

 opportunity during the early stages of their free living existence while they are actively feeding upon 

 the organic materials in the medium, commonly fecal matter which surrounds them, to pick up injurious 

 microorganisms, and these it is quite conceivable may be carried with them on their later migrations 

 and finally deposited where damage will result. Looss (1911, Rec. Egypt. Govt. School Med., Cairo, 

 v. 4, p. 557), for example, suggests that Ancylostoma larvae which have developed in feces might retain 

 some bacteria in their intestine and evacuate these as soon as they arrive in the body of their host, and 

 that this if it occurred might have something to do with the skin lesions which accompany Ancylostoma 

 infections. 



Returning to the nematodes in the thyroid of the dog, it has not seemed advisable to venture an 

 opinion as to the genus or even the family to which the parasites may belong. In order that they may 

 not be left nameless I have designated them as Agamonematodum gaylordi, thus placing them in a col- 

 lective group, which is used for convenience of reference to include various immature nematodes, 

 whose sexually mature stage is undetermined. The following brief description is based on an individual 

 the anterior portion of which is present in the sections on a slide labeled " Dog 17. K. 1-22-12.20, Nem. 

 2". (Fig. 123.) 



AGAMONEMATODUM GAYLORDI. 



Length uncertain, but apparently less than i millimeter; maximum width 35;*.. Head apparently 

 with 3 lips, each supplied with a small papilla. Diameter of head at level of papillae sofi, increasing to 

 24^ at a distance of 2o/ from the anterior end, then rather suddenly constricted to 20/1, after which the 

 diameter of the body gradually increases, reaching 32;* at the level of the nerve ring, which is located 

 about ioo/i from the anterior end of the body. Mouth very small, communicating directly, without 

 intervening larynx or mouth capsule, with the esophagus. Esophagus near its anterior end 

 measures about i6// in diameter, is then constricted slightly, corresponding with the constriction of 

 the body, and gradually increases again in diameter, attaining a size of about i8/t in the neighborhood of 

 the nerve ring. Length of esophagus uncertain, but exceeds i6o/z. The anterior end of the body is 

 supplied with narrow lateral cuticular wings, which extend posteriorly an unknown distance beyond 

 the esophageal region. 



Host. Dog (Canis familiar is}. 



Location. Thyroid gland in small tubercles. 



Locality. Craig Brook, Me. 



The nematodes were not found in the two dogs examined in 1910, one of which had 

 marked thyroid hyperplasia and the other a nearly normal gland, but serial sections were 

 not available. In all (3) of the puppies which had marked hyperplasia and were given 

 drinking water in which were suspended scrapings (dog 16, dog 17, and dog 22) nema- 

 todes are present. In the white mongrel adult dog with the highest degree of diffuse 

 parenchymatous hyperplasia and degeneration (dog 18) they are also present. In the 

 control for this dog, the mother of the puppies, which received boiled water (dog 19), 

 they are not present. In the control puppy no. 21, which received boiled water, they 



