500 BUI^I,ETIN OF THE BUREAU OF FISHERIES. 



worm. (Fig. 124.) Occasional tubercles will be encountered in which either the head 

 (fig. 123) or tail of this worm lies near the periphery, and in some instances a fully 

 formed tubercle has been encountered with cross sections of the worm lying without 

 the connective-tissue capsule usually coiled in undulating fashion. (Fig. 122.) The 

 worms appear to be of the same species. For the purpose of identification, sections of 

 the worms have been submitted to B. H. Ransom, Chief of the Zoological Division of 

 the Bureau of Animal Industry of the United States Department of Agriculture at 

 Washington. We are indebted to Dr. Ransom for the following notes: 



After examining the preparations I fail to identify the parasite to which you call attention with 

 any known species. As it is quite different from a hookworm larva it is not Ancylostoma caninum or 

 any other species of hookworm, a possibility which would perhaps first suggest itself, inasmuch as the 

 larval stages of Ancylostoma en route to the alimentary tract are likely to be found in various tissues, 

 though apparently they have not yet been noted in the thyroid gland. As to other possibilities, so 

 far as I have been able to determine, no nematode has been recorded from the thyroid gland of dogs. 

 Furthermore, the form in question does not agree in morphology with any adequately described nema- 

 tode known to occur in the dog in any part of the body. 



The nematodes in this case, which are sexually undeveloped, may be (i) immature stages of some 

 species which occur in its adult stage in the dog and whose larvae after gaining entrance to the body 

 perform more or less extensive migrations before reaching their fir.al location, and would thus be com- 

 parable to Ancylostoma, whose larv^ regularly migrate from tlie skin to the digestive tract, or to Spirop- 

 tera sanguinohnta, whose larvae, it is stated, sometimes migrate from the digestive tract to the blood 

 vessels and other rather remote locations where development to maturity may occur; (2) they may 

 conceivably belong to some species like Ollulanus tricuspis, whose young, according to Leuckart, may 

 either pass out of the body to become encysted in an intermediate host or penetrate into various tissues 

 of the original host and become encysted in the manner of Trichinella; (3) they may be the larval stage 

 of some species whose adult stage occurs in another host, the dog acting as a true though perhaps unusual 

 intermediate host; or (4) they may be present in the dog as the result of an accidental infection entirely 

 outside the normal life cycle, this case being comparable to that of the infestation of mice and other 

 animals with the larva of Spiroptera sanguinolenta to which Seurat (1912, Compt. rend. Soc. de biol., 

 Paris, V. 73, p. 279) has called attention. This autlior notes that these larvae which are found in cock- 

 roaches, instead of developing to maturity as when fed to dogs, if fed to white mice pass through the 

 wall of the digestive tract and become encapsuled in various organs without undergoing further devel- 

 opment. The possibility last suggested (4) is also comparable to that of the migrations of the larvse 

 of Ancylostoma duodcnale, a human parasite, in dogs. The larvae of this species penetrate the skin of 

 dogs and in course of time may reach the intestine, undergoing a partial development which, however, 

 falls short of maturity. 



As a rule when nematodes or other parasites are found in a given host it is to be presumed that 

 the animal is playing the part of a true host and that there is a more or less complete adaptation between 

 the host on one hand and the parasite on the other. The possibility, however, should not be lost sight 

 of that larval nematodes of an unknown species found in a certain host, or of a known species found 

 in an unusual host, may represent individuals which have gone astray so far as the possibility of com- 

 pleting their normal life cycle is concerned. It is apparently true that nematodes which tlius go astray 

 usually die before there is any development or any invasion of the tissues of the animal. Tliat is, 

 nematodes entering the digestive tract of an animal which is unsuitable as a host as a rule quickly 

 succumb without doing any damage. This is, however, not the case with all species, for example,' 

 Spiroptera sanguinolenta in mice, as noted above. (Similarly in the case of nematodes whose normal 

 mode of entrance is through the skin it is to be presumed that they will not even enter the skin of an 

 unsuitable host, but such occurrences may not be very unusual. The case of Ancylostoma duodcnale 

 already mentioned, and that of Strongyloides sicrcoralis, another human parasite, which behaves much 



