In 1865, Leuckart described from the stomach of the domestic cat, a minute bursate worm which he named Ollulanus tricuspis. His original description was somewhat scanty, but it was amplified in later years (1867–1876). As this work is scattered throughout many pages, the following is a brief resumé of Leuckart's theory.

He was struck by the fact, that being viviparous in habit, it resembled Trichinella spiralis, but recognised that several fundamental differences existed between them. Ollulanus never produced more than three larvae at a time from relatively large eggs, about 60μ to 120μ long; whereas Trichinella produced numerous larvae with small eggs about 35μ long. He found what he believed were the free larvae of Ollulanus, which measured about 320μ long by 15μ wide, had a truncated oral extremity and a short tail which ended in a short S-shaped tip (Fig. 1, a). The oesophagus was between one third and one half of the total length of the intestine; several transparent vesicles could be seen at its clubshaped posterior extremity. Although there are seldom more than three embryos inside the female, larvae were usually, found in large numbers throughout the whole intestinal tract of the host, as well as encysted (in cysts ·15 to ·2 mm. in diameter) on various internal organs. The cyst wall had a connective tissue-like structure of such thickness that it might be three or four times the diameter of the enclosed space.