Some time ago Mr. J. H. Spitzly kindly forwarded to our Museum a few bottles with parasitic worms, collected by him in Surinam. Among them there was a bottle, containing some Nematodes found in the heart of a young female Jaguar, that was killed by a hunter. In reference to these parasites Mr. Spitzly wrote to me: »on incising the remarkably thin walls of the right ventricle, I was astonished to find the whole cavity fully packed with long white worms, laying in bundles more or less parallel to each other in the direction of heart’s apex to endings of pulmonary arteries. By slitting open the pulmonary arteries I found that some of them extended from the heart along the arteries far into the substance of the lungs.” These worms bear a great resemblance to Filaria inmitis Leidy, observed by several investigators in the right ventricle and the pulmonary arteries of our common dog. Having no individuals of this species at my disposal, the specimens could only be identified from the short description, published by Schneider in his »Monographie der Nematoden” pag. 87 1); therefore the Jaguar-filaria’s afterwards perhaps may prove to belong to another species. However because Nematodes never have been mentioned from the heart of Felis onca, as far I am aware off, I thought it not without interest to call the attention of helminthologists on this fact.