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BULIvETiN OE 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 final location, and would thus be com- 
parable to Ancylostoma, whose larvae regularly migrate from the skin to the digestive tract, or to Spirop- 
tera sanguinolenta, 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 tmusual 
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 larvae of Spiroptera sanguinolenta to which Seurat (1912, Compt. rend. Soc. de biol., 
Paris, V. 73, p. 279) has called attention. This author 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 larvae 
of Ancylostoma duodenale, 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 thus go astray 
usually die before there is any development or any invasion of the tissues of the animal. That 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 duodenale 
already mentioned, and that of Strongyloides stercoralis, another human parasite, which behaves much 
