The two flies Fannia canicularis Linn, and F. scalaris Fab. are, on account of their habits, of considerable economic importance in their relation to man. It is therefore desirable that those engaged in public health and medical work and others should have a knowledge of the breeding and other habits of these flies, which they are certain to meet in their work under circumstances of varying importance. The inquiry of which this account is the result was undertaken several years ago at the request of Dr Monckton Copeman in connection with the Local Government Board's inquiry on the carriage of infection by flies in the reports of which a portion of this paper has been included. Owing to my removal from England to Canada in 1909 and subsequent pressure of work, its completion was delayed.

In 1892 Louis Léger described three species of gregarine from the alimentary tract of the larva of Tipula: Actinocephalus tipulae, Clepsidrina longa, and Eirmocystis ventricosa2.

The haemogregarine which is the subject of the present communication was obtained in material collected by me during two voyages made in a trawler in July 1910, round the Shetlands and the north coast of Scotland. It was found in large adult specimens of catfish (Anarrhichas lupus), taken by otter trawl from a depth of 50 to 80 fathoms, in the vicinity of Fair Isle and Foula, and on Whitenhead Bank about nine miles to the N.N.E. of Cape Wrath. Catfish taken near Rhona and Sulisker in the Atlantic showed no infection, but the number of fish examined was so small that one could not assume the infection to be absent in this locality.

In September, 1908, an opportunity was afforded me of examining some of the larger food-fishes brought in to Aberdeen fish market. For this I have to thank the courtesy of Professor J. Arthur Thomson, who kindly provided the necessary laboratory accommodation, and was of great assistance to me in various other directions. I have also to thank the Government Grant Committee of the Royal Society for defraying the expenses of procuring specimens.

1. All stages of Argas persicus are negatively phototropic. In addition, they are also susceptible to pronounced differences in the intensity of the illumination and select the darker places.

2. In the gorged state, the ticks are slightly positively geotropic. In the unfed state, this property is not developed.

3. At all stages the tick endeavours to bring as much of its surface as possible in contact with its surroundings.

4. A. persicus is attracted by heat.

5. In all stages an olfactory sense is well developed.

6. “Haller's organ” is olfactory in function and constitutes a means by which a tick is able to recognise its host. By depriving ticks of this organ it is possible by suitable means to cause them to feed on media other than blood, thus showing that a sense of taste is absent. Argas persicus, Ornithodorus moubata and Hyalomma aegyptium have all given similar results with regard to the latter point and we believe that this constitutes a method by which perhaps other blood-sucking arthropods, after being deprived of the organ or organs necessary for the recognition of their hosts, may be made to feed on any desired medium.

The trematode described in this paper was found by Dr Alexander Brown, British Central Africa, in the stomach of a Rhodesian hartebeest (Bubalis sp.). About 120 specimens were collected and placed at my disposal for investigation by Dr John Rennie, Lecturer on Parasitology in this University, to whom I am much indebted for the use of the interesting material. The specimens proved to belong to a new species to which the name Gastrothylax bubalis has been given. Although a fuller knowledge of recorded species rather than the recovery of new trematodes is to be desired, it is hoped that the description of this parasite may be interesting from the fact that the genus includes only ten other known species.