1. The period which elapses between a blood-meal and oviposition on the part of the female bed-bug affects the duration of the egg stage. Eggs laid soon after the meal take longer to hatch than those laid later. It is supposed that embryonic development of eggs inside the female occurs at a rate relatively greater than that of oviposition.

2. Atmospheric humidity is without effect on the duration of the egg stage. Although the temperature-velocity graph appears to be fairly linear between 18 and 30° C. the thermal constants show considerable variation.

3. A daily alternation of temperature with a range of 10° C, between the threshold and optimum temperatures results in an acceleration of development; this can, however, be accounted for by the non-linearity of the temperature-velocity relationship, if the usual methods of thermal summation are used.

4. Eggs have been exposed to temperatures between 1 and 12° C. and the time taken to hatch on subsequent incubation at 23° C. has been ascertained. When these times are compared with times for hatching of control eggs kept at 23° C. from oviposition there is some evidence that a slight amount of development may occur at as low a temperature as 4° C.; i.e. 9° below the developmental-hatching threshold. Times after exposure are shorter than times for control eggs.

5. Thermal summation, however, suggests that temperatures between 13 and 11·7° C. result in a retardation of development since the times after exposure at which hatching occurs at 23° C. are longer than would be expected.

6. The method of thermal summation is criticized mainly on the grounds that it assumes that a temperature has the same accelerating effect on all stages of embryonic development. A retardation of development such as that mentioned in the preceding paragraph may be either a true retardation or due to errors resulting from the assumption that the reciprocal of the time for complete development represents the true amount of daily development at all stages of embryonic growth.

7. The lowest constant temperature at which complete development with hatching, of eggs laid at 23° C, can occur is 13° C. I have called this temperature the developmental-hatching threshold. The developmental threshold may be as low as 4° C, while the hatching threshold is at approximately 8° C.

8. Alternating temperatures such as occur in English houses are unlikely to affect the position of the developmental-hatching threshold. Atmospheric humidity does, however, affect it and 75–90% r.h. appear to be the only humidities at which development with hatching can take place at a constant temperature of 13° C.

9. Mortalities near the developmental-hatching threshold appear to depend also on the temperature at which eggs are laid (or perhaps the temperatures at which they develop within the female). Eggs laid at 15° C. and incubated at 15° C. and 7% r.h. suffer 97·1% mortality while those laid at 23° C. and incubated under identical conditions have 32·9% mortality.

10. If eggs are laid at 23° C. and are incubated at 15, 18 and 23° C. until nearly ready to hatch, the percentage hatch at temperatures near the batching threshold is higher with those eggs previously kept at 18° C. than with those from 15 or from 23° C. At 8° C, the lowest observed temperature for hatching, preliminary incubation at 15° C. is probably more favourable than one at 23° C.

11. Mortality of eggs above 13° C. is only slightly affected by atmospheric humidity over the optimal range. But the effects are more noticeable near the upper and lower temperature limits. 99–100% r.h. appears to be associated with a higher mortality than 90% r.h. The extreme temperature limits for eggs laid at 23° C. are 13 and 37° C. With eggs laid at 15° C. the range is restricted at both upper and lower temperature limits compared with the range for eggs laid at 23° C. The temperature of oviposition, whether it is 15 or 25° C, seems to make no difference to mortalities between 18 and 28° C.

12. The mortalities of eggs exposed for varying periods to temperatures between 1 and 13° C. and various humidities are discussed. By means of probits estimates of the times for 50 and 99·99% mortalities have been made for each of the temperature and humidity combinations.

13. Exposure for 50% mortality is affected slightly by humidity below 13° C, but no simple law relating survival to humidity has been found either above or below 13° C. Variations in temperature within the range 0—34° C. are likely to influence survival more than the humidity variations possible within this temperature range.

14. At constant saturation deficiencies the eggs survive longer at the higher temperatures between 1 and 13° C. The median exposure for death (i.e. exposure for 50% mortality) increases by 1·5–1·8 days per 1° C. rise of temperature.

15. The scatter of mortalities about the median exposure for death as measured by the regression coefficient of probits on exposure times is slightly influenced by humidity, but is not affected by temperatures between 1 and 13° C. Much of the variation in the slopes of the mortality curves is thought to be due to inherent variation in the eggs themselves.

16. With eggs laid at 23° C. and exposed to temperatures below 13° C. the longest exposure necessary to produce 99·99% mortality (as judged by subsequent incubation at 23° C.) was estimated at 79.8 days. This occurred at 12·1° C. and 73% r.h. The actual observed times for exposure for 100% mortality are somewhat shorter than the estimated times.

17. Eggs with embryos in an advanced state of development are more quickly killed by exposure to 7·7° C. and 90% r.h. than are newly laid eggs.

18. Ovipositional temperatures of 15, 18 and 23° C. produced no different effects on the mortality rates of eggs exposed to 10° C. and 90% r.h.

19. Future problems and the ecological significance of the experimental results are discussed.

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.

1. Rickettsia-like bodies are recorded from the reduviid bug, Triatoma rubrofasciata.

2. These Rickettsiae are capable of being transmitted hereditarily and have been found in the unhatched embryos and larvae of the bug.

3. They produce pathological lesions in laboratory animals and can be maintained for at least five passages through guinea-pigs.

Although the following Notes may appear elementary to practised writers, over thirty years' experience as an editor has convinced me that many authors need guidance in the preparation of their manuscripts and illustrations for publication and in dealing with their proofs.

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.

Argulus Foliaceus has a remarkably wide distribution, and is found throughout Europe. A. coregoni, which is another European form of the Argulidae, has been recorded in England from such localities as the Birmingham Canal; Barble, Leicestershire; Berkshire Trout Farm; the River Wharfe, Yorkshire; Tring Reservoirs; the Thames; the River Frome in Somerset; and the River Lune.

1. Malaria parasites of the Plasmodium ovale type are recorded from Mauritius.

2. The chief differential characters between P. vivax and P. ovale are given.

3. Stress is laid on the difficulty of correctly diagnosing such an infection using the thick smear method.

The small collection of avian tapeworms from Antigua which, is the subject of the present paper was sent to us for identification, through Prof. R. T. Leiper, by Mr L. R. Hutson, Veterinary Officer, Antigua, to whom we tender our sincerest thanks.

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).

1. The anatomy of the adult miracidium of Parorchis acanthus is described.

2. Development of the miracidium and of the succeeding larval stages has been followed.

3. Cleavage of the fertilized egg gives rise to an ectodermal and a propagatory cell. The former gives rise to the soma, and the latter, after contributing a few small cells to the body of the miracidium, becomes the germ cell.

4. This germ cell develops in the same way into the first generation redia while still in the body of the miracidium.

5. The fully formed miracidium contains a single fully formed redia when it penetrates the intermediate molluscan host.

6. In the intermediate host the miracidium disintegrates and second generation rediae are formed from the germ cells in the body cavity of the parent redia.

7. The germ cells in the body cavity of the daughter redia give rise to cercariae by a similar process of embryonic development to that found in preceding generations.

8. The germ cells in the cercariae become differentiated into the adult genitalia.

9. No evidence has been found to show that rediae or cercariae are derived from cells in the wall of the redia.

10. No ovary, maturation process, parthenogenesis, or fertilization takes place in any of the larval stages, but germinal lineage is apparent throughout the life cycle.

Aplopabaksis filum (Goeze, 1782), A. clerci Yamaguti, 1935, and A. brachyphallos (Krabbe, 1869) are closely related species that are distinguishable mainly on anatomical characters, their scolex structures being remarkably uniform both in size and form. This opportunity is taken of defining the main diagnostic characters of the three species from an investigation of material collected in the Aberystwyth area of Wales.

1. During the period November 1936 to February 1937, eighty rabbits were examined, whilst from August 1937 to July 1938 another 446 were examined for nematodes. The following nematodes were found: Graphidium strigosum, Passalurus ambiguus, Trichostrongylus retortaeformis.

2. The incidence of the above three nematodes is given, and their seasonal incidence is discussed, with special reference to its ecological implication.

3. Evidence of host and age resistance is also demonstrated in infections with Graphidium strigosum, Passalarus ambiguus and Trichostrongylus retortaeformis.

4. The proportion of the sexes in Graphidium strigosum was found to be constant during both periods. The percentage of males in 1936–7 was 45·6 and 45·96 in 1937–8. In Passalurus ambiguus, however, the proportion of the sexes varied to a large extent.

1. It was found that larvae of the genera Trichostrongylus, Haemonchus, Ostertagia and Chabertia migrated upwards on the blades of sedge (Kylinga sp.) and of rye grass (Lolium perenne) in greatest numbers when subjected to a light of an intensity about 62 f.c.

2. Moisture on the grass was found to favour laval migration. More than 0·12 ml. of water per sq. cm. of soil surface, however, retarded movement. More than 0·2 ml. per sq. cm. tended to prevent larval migration up the grass.

3. Of the genera examined Ostertagia spp. were most favoured by the presence of moisture on the grass; Haemonchus contortus was most hindered by its presence.

4. Increasing quantities of moisture in the soil up to 85% saturation assisted larvae to move on to the grass. Above this value larval migration was retarded.

5. Ostertagia spp. were best able to migrate from wet soil while Haemonchus contortus was least able to migrate from wet soil.

6. It was found that the presence of water on the soil surface tended to lessen the ability of larvae to move on to the grass.

7. Haemonchus contortus was found to migrate on relatively dry grass at a faster rate than Trichostrongylus spp. and Ostertagia spp.

8. In the temperature range examined larvae were found to move up the grass in largest numbers at 5 and 45° C.

9. Haemonchus contortus was the most active species at higher temperatures.

10. The cycle of larval movement during the day, under conditions approximating to those of the field, was investigated. The greatest number of larvae were recovered from the grass in early morning. Reactions in the evening were much less marked.

From 1931 to the middle of 1936 we occasionally examined the gut contents of the centipede Cormocephalus dentipes, procured from Calcutta and its suburbs. In the intestine we have often found a coccidium belonging to the genus Adelina. Species of Adelina are on record from arthropod and annelid hosts; but since Schellack (1913) described in detail the life history of A. dimidiata from Scolopendra cingulata, no account of any other species from a myriapod has been given.

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.

1. Between November 1936 and February 1937, ninety-six rabbits were examined, whilst between August 1937 and July 1938, 446 rabbits were examined for cestode parasites. The rabbits were obtained from the same area.

2. The rabbits were infected with the following cestodes to the extent given, for the two periods respectively:

3. Two species of the genus Hymenolepis are recorded for the first time from the rabbit, and they are briefly described.

4. The seasonal fluctuations in the incidence of the above cestodes are discussed.

5. The span of life of both Cittotaenia pectinata and C. denticulata is seen to be not greater than 10 months, and evidence is given to show that the intermediate host of C. denticulata is available between April and December, and that of C. pectinata from August to April.

6. Evidence of host and age resistance is demonstrated in Cysticercus pisiformis.

If the normal molluscan host of Fasciola were a species of Lymnaea it should be possible readily to produce experimental infection in that species. Although adult flukes have been reared from larvae found naturally in different species of Lymnaea in various countries, great difficulty has been experienced in producing experimental infection of these same species of Lymnaea. In fact, although the factors governing the successful completion of the life cycle are not known, the ease with which, according to text-books, the cycle may be followed experimentally, is contrary to experience in both Europe and warmer climates.

An amoeba was found in the faeces of ten out of fourteen English goats from three different localities.

The amoeba, of which a detailed description is given, is morphologically identical with Entamoeba debliecki of the pig and is therefore included in the same species.

A statistical analysis shows that the caprine strains of E. debliecki comprise two races distinguishable from one another by the size of their cysts but identical in all other features.

The caprine amoeba appears to be non-pathogenic.

In view of their bearing upon the systematic position of the parasite of the goat, a critical review is given of the data concerning the various amoebae previously recorded from the pig, goat and some other ruminants.

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.

In the present paper I have pleasure in describing three new species of mites of the genus Myobia, three new species of Listrophoroides, a new species of Listrophorus, and a new genus of Laelaptinae. Also there is the description of the female of Stanley Hirst's species Listrophorus bothae.