PART III.] Imperfect Stage of Development of the Filarice in Blood. 547 



afterwards, detected in the bodies of the animals without having undergone any apparent 

 change. 



/ /' Where the true habitat of these embryos may be is as yet unknown. Whether, 

 after a lengthened sojourn in moist earth, or in water, or in the intestinal canal of 

 some creature other than the dog, the embryo escapes and undergoes developmental 

 changes, must be left for future inquiry, as must also the direct proof that the 

 microscopic worms in the blood of the pariah dog are the brood of the Filarice san- I .■ 

 gumolentce which may be lodged in the wall of the aorta or oesophagus, or in some// 

 other tissue, glandular or connective, about the base of the heart or elsewhere. All 

 that I can say is that all my attempts at finding any other mature nematode in the 

 vascular system of dogs affected with Hsematozoa have proved fruitless, and I have made 

 careful examinations — macroscopic and microscopic — of every tissue and organ of the 

 bodies of several animals, and followed the ramifications of the various arteries and veins 

 in the trunk and in the extremities. On one occasion, no trace of any mature parasite \ 

 in a Hsematozoa-affected dog could be found, but it is quite possible that the parent 

 may have escaped detection by being lodged in some out-of-the-way tissue in the 1 

 body, and one worm might contribute many thousands of ova ; or the worm, after 

 depositing its ova, may have taken its departure, or have died, and become disintegrated. 

 The scarred and sacculated condition of the aorta, already described, which is sometimes 

 observed unassociated with any parasite at the time of the examination, shows that 

 the worm that produced the lesion may altogether disappear. 



Moreover, we require to know far more than is at present known concerning the 

 development and parentage of these canine microscopic blood-worms, before anything 

 definite can be stated with reference to their relationship to similar organisms found 

 in the blood of dogs in France, China, Japan, and America. 



So far as I am aware, Dr. Spencer Cobbold is the only author who has suggested 

 that the young of the Filarice sanguinolentce may possibly find their way into the blood * 

 — a suggestion which is the more noteworthy, seeing that, to the best of my knowledge, 

 no observations had been recorded showing that this nematode ever penetrated the 

 arteries. 



Although I have not been able to keep individual dogs affected with this Hsematozoon 

 during any lengthened period, still there can hardly be any doubt but that, as has 

 already been shown with reference to the human Hsematozoon and been previously re- 

 marked concerning Haematozoa in animals generally,! these microscopic worms may exist 

 for a considerable time in the blood (unaltered after having attained a certain, very 

 imperfect stage of development), showing that they were not in the place or fluid 

 fitted for their growth. Their presence in the blood, it may therefore be presumed, is 

 accidental, or if not exactly accidental, the young brood requires at least to be transferred 

 to some other habitat before undergoing even the most elementary morphological changes. 



* Entozoa : an Introduction to the Study of Helminthology, London, 1864 p. 95. Supplement to ditto, p. 63. 

 t In dogs in France and China ; in the frog ; and in the crow. — Leuckart : Oj}. cit., p. 102. 



