1. With unfed 1st instars the relation between mean length of life and saturation deficit at constant temperatures between 7 and 15° C. at relative humidities between 7 and 90% is hyperbolic. The relationship becomes more linear at higher temperatures.

At constant saturation deficits insects live longer at 15° C. than at lower temperatures. Longevity also decreases with rise of temperature above approximately 15° C.

2. In general, the longevity curves, except for those at temperatures below 15° C., bear a very similar relation to saturation deficit and to each other as the reciprocal curves for rate of water-loss at the different temperatures.

The influence of climatic factors on longevity at constant temperatures is discussed at length and it is concluded that over much of the temperature and humidity range survival time is limited by water-loss. At the higher humidities it is thought that either food, or perhaps an excessive accumulation of water within the insect, limits survival and causes a departure from the hyperbolic relation of longevity to saturation deficit.

3. The effects on longevity of a single meal are discussed. The principal effect of a blood meal is to increase the time of survival. But the factors which limit survival at different humidities appear to be the same as with unfed bugs, except at high humidities below about 15° C.

4.Mellanby's data on the rate of water-loss from fasting adult bed-bugs is analysed. It is found that the rate of water-loss is directly proportional to saturation deficit at constant temperatures between 8 and 37° C. and between 0 and 90% r.h. Although the rate may always be directly proportional to saturation deficit, the expression is not always constant.

Rate = K + b (saturation deficit), where K varies with temperature and b remains constant.

5. Longevity in relation to host blood is discussed. Rabbit blood appears to be slightly less favourable to survival than human blood.

6. If bugs are allowed to feed to repletion, longevity is not correlated with the size of the meal, nor with the weight of the unfed insect.

Virgin females live longer than mated ones, but no effects of mating on survival were noticed with males. Mated males tend to outlive mated females except at very low temperatures: virgin females live longer than unmated males.

7. The results of other workers and the possible causes of some discrepancies are discussed.

8. The maximum survival times of bugs are listed. Adults and 5th instars live longer than other stages. In a house which has remained empty for a long time it is probable that 5th instars and adults, particularly unmated female adults, would predominate in the population.

The longest observed survival was between 562 and 572 days.

This description is based upon a study of six identical monogenetic trematodes which were collected from the gills of the tunny by Mr F. S. Russell, F.R.S., and which were presented to the writer for identification. They had been fixed already in a flexed but otherwise excellent condition in Bouin's fluid on cleanly cut pieces of gill tissue to which they were adherent. Two of the specimens were cut into serial sections while still in situ on the gills, and the remaining specimens were detached carefully from the gills and examined whole. Gill tissue of the fish in the vicinity of the parasite was seen to be modified and such observations as could be made on the effect of the parasite on the tissues of the host have been recorded.

The following observations were made upon serial sections of a new monogenetic trematode, Hexacotyle extensicauda, which the writer has described in a previous paper (Dawes, 1940).

The author has examined 1437 crops of hair, removed from adult or adolescent males on admission to jail, at Cannanore, South India. There is a high positive correlation between weight of hair and rate of infestation with head-lice, men with less than 10 g. of hair being 14·6% infested, those with 10–19·9 g. 39·9%, and those with over 20 g. 56–59%.

There appears to be a negative correlation with age, but this seems to be due to the older men having less hair: if one standardizes hair weight there is no tendency for older men to be less infested than younger. In a similar way, the large differences in rate of infestation between different religious groups appear to be due to a great extent (but not entirely) to differences in hair weight.

No evidence was found that rate of infestation is different at different times of year. The rates in the rainy and dry seasons scarcely differ, in spite of the intensity of the rain, and of the fact that the rainless period lasts for six months. It is possible that there is a long-period, secular change in rate of infestation.

The precise biology of the body louse under experimental conditions is a subject not sufficiently explored. At present we need quantitative information about the possible rate of increase of the insect: we must also know about the normal biology in studying insecticides. The present moment is therefore an appropriate one for publishing certain experiments which have occupied a part of my time for the last 4 years.

1. The feeding of the tick Ixodes ricinus was studied in relation to the reproductive condition of the host, in this case the hedgehog Erinaceus europaeus.

2. Hedgehogs in hibernation, in full breeding condition, and injected with male and female sex hormones, were parasitized with unfed nymphs and female ticks in midwinter.

3. Attachment and engorgement of the ticks was successfully accomplished on both sexually active and inactive hosts. The longer time required to complete engorgement on the hibernating hedgehogs may be explained by their lower blood temperature.

4. Parasitization by this tick does not appear to be related to the reproductive condition of the host animal, and the amount of sex hormone in the host's blood has no apparent immediate effect on the fecundity of the tick.

The genus Microcotyle of the order Monogenea is a large one, containing about forty species, and it is well summarized by MacCallum (1913, 1915).

An account is given of ultrafiltration studies with Nicotiana virus 11 (tobacco necrosis virus). It is shown that though the filtration end-point is about 40 mμ, there is invariably a sharp drop in the local lesion counts between the membrane pore sizes 250 and 125 mμ. This phenomenon shows itself as a “bench” or shelf with an upward trend in the filtration curve (see Text-fig. 1, curve A). A number of possible explanations are given. The fact that increasing dilution raises the height of the bench leads to the deduction that large particles are breaking up into smaller ones, the larger particles being aggregates of the smaller. Experiments on resuspension of virus inside the filter and fractional filtration support the same conclusion.

From the filtration end-point the particle size of the virus is computed to be between 13 and 20 mμ.

Seven species of marine fishes and three of fresh or brackish water Canadian fishes have yielded new or known Myxosporidia. The marine fishes were from St Andrews, New Brunswick and Halifax, Nova Scotia, places 250–275 miles apart by sea, and from the Labrador coast. The brackish and freshwater fishes were obtained in Montreal and the Salmon River, Nova Scotia.

Descriptions and illustrations are given of the morphology of five new species of Myxosporidia: Ceratomyxa urophysis, Myxoproteus myoxocephali, Myxidium myoxocephali, Myxosoma diaphana and Henneguya amiae.

Chloromyxum leydigi Mingazzini, C. granulosum Davis, Myxidium lieberkuhni Bütschli, Myxidium gadi Georgévitch and Zschokkella hildae Auerbach are recorded from new piscine hosts in Canada.

Some effects of the Myxosporidian infections, both macroscopic and microscopic, on their hosts are considered. Comparison of the effects of similar infections of Myxosporidia on allied fishes in Normandy and Eastern Canada has shown a general similarity between them.

The economic importance of some Myxosporidian infections of the edible fish examined is shown by parasitism of the cod, haddock and sculpin. Amia calva is also used for food in Montreal. The possibility of edible fishes acquiring Myxosporidian infections by way of their food is noted, with reference to the host-specificity of the Myxosporidia of Fundulus heteroclitus described by Bond.

The influence of environment on and powers of adaptation to different habitats exhibited by certain Myxosporidia is discussed.

Some remarks are made on the zoogeographical distribution of certain Myxosporidia and their piscine hosts.