Owing to the lack of adequate descriptions and figures, the majority of the members of the Genus Capillaria are extremely difficult to identify. This is no doubt due, to some extent, to the fact that the worms are so slender that certain morphological features upon which species can be separated are difficult to observe without a very close examination of the worms under high magnification.

During recent years the compounds belonging to the resorcinol series have acquired considerable importance as germicides, and among these compounds the hexyl derivative has provided the optimum working value. While this is reasonably active, a sufficient quantity can be obtained in solution for administration.

The following material was sent to the Department of Helminthology of the London School of Hygiene and Tropical Medicine in three groups; two lots coming from Mr. Aneurin Lewis, of the Veterinary Research Station at Kabete, Kenya Colony, and the third lot from the Director of Veterinary Services, Uganda. For this latter, the writer is indebted to the Imperial Bureau of Agricultural Parasitology. The major part of the material was placed at his disposal by Professor R. T. Leiper, F.R.S., to whom he wishes to express his sincere thanks.

In 1890, Müller described, from the lung of the cat, a species of nematode which is now known as Aelurostrongylus abstrusus. In 1928, I was able to show that its true habitat was not the lung substance, but the pulmonary artery and its branches, and that its pathogenic action, was mainly, if not entirely, due to the presence of the developing eggs and larvae distributed throughout the lung tissue by the blood stream.