The following descriptions axe based on material collected or reared by the author, together with specimens reared from host-plant material collected by colleagues to whom the author's thanks are due.

From the descriptions it will be further evident that the generic location of new species is still difficult, but this state of affairs can only be remedied by a monographic revision of the African Trypetidae. It is felt, however, that although the author has such a work in progress, it is not desirable to hurry publication. Delay is advisable, especially in view of the number of new species continually being found, and the frequent need for the formation of new genera.

Types of the new species are in the author's collection ; paratypes so far as available will be placed in the British Museum.

I am indebted to the Imperial Institute of Entomology and to Mr. F. Laing, of the British Museum, for submitting to me for classification a small collection of Thysanoptera from the Waite Agricultural Research Institute, Glen Osmond, South Australia. All measurements in this paper are in μ.

The law of population, as finally expounded by Malthus, conceives that increase depends upon the availability of food or upon the ease, difficulty, or ability of procuring it. The consideration of the action of parasites from this point of view, I believe, is of interest and importance, both from the economic and biological standpoints.

Eurytoma verbena, sp. n.

♀♂. Black ; abdomen sometimes a little reddish on the sides. Antennae dark brown ; pedicel slightly yellow below. Wings whitish, with the veins very clear yellow. Legs with coxae and femora black, the latter sometimes a little reddish ; tibiae red in the middle, often mixed with black, especially at the hind tibiae ; knees, base and tip of tibiae, and the tarsi whitish.

♀. Head rugulose, face covered with white ciliae, with a carina between the base of antennae and the clypeus, and weaker striae diverging from the mouth. Antennal furrow rather deep, bordered by a carina and reaching almost to the median ocellus. Cheeks as long as half the length of the eyes, finely rugulose. Antennae inserted in the middle of the face ; scape short, reaching very little beyond the top of the antennal furrow ; pedicel not longer than broad ; annelli very small ; funicle joints longer than broad, the 1st almost twice, the 2nd about 1·5 times longer than broad, the following gradually shorter.

Thorax more strongly sculptured than the head, reticulate. Scutellum protruding a little above the postscutellum, which is hidden, and the propodeon ; this latter, seen from the side, has the posterior margin almost vertical. Mesopleurae finely punctate, with some short horizontal striae ; episternum transversely striate, but the striae not reaching to the hind margin, along which it is punctate, like the mesopleurae.

(1) A. elutus females in Palestine show seasonal variations of fertility, but these do not appear to explain fully the distribution of adults throughout the year.

(2) Females of the overwintering generations show low fertility. This depends probably on conditions of larval life.

(3) The seasonal changes in the egg of A. elutus in Palestine are due to temperature variations. It is suggested that these changes are protective adaptations against cold in winter and excessive heat and irradiation in summer.

(4) The entering of the hibernation stage of A. elutus in Palestine cannot be considered as a pure consequence of the low temperature in autumn, since spring activity begins at a much lower temperature.

(5) During hibernation the females feed, but do not bring eggs to maturity ; the blood is used for fat accumulation.

(6) During the second half of the hibernation period the females lose their reserve materials.

(7) Full fat females starved in the laboratory lose their fat-body reserves, and simultaneously their ovaries develop to stage 2. Under the prevailing temperature the process requires about 3 weeks.

(8) A slow development of the ovary is going on during hibernation, but never proceeds beyond the second stage. The ovaries in a large percentage of females reach this stage at all times when reactivity occurs at the end of the hibernation period.

Rhembastus pomorum, sp. n. (fig. l).

Oblong-ovate, metallic dark blue ; clypeus, antennae and legs fulvous ; prothorax finely and remotely punctured ; elytra finely punctate-striate, with the interstices glabrous. Length, 4 mm.

Since a fairly extensive collection of the Braconid genus Spathius, largely comprised of bred series of new species, had lately been received for identification by the Imperial Institute of Entomology, and since there were various species in the British Museum awaiting description, it was considered opportune that I should attempt some sort of revision of this comparatively little worked but nevertheless quite interesting group : it is hoped to publish my results shortly. In the meanwhile, however, the following descriptions are presented since most of these names are required at an early date for inclusion in a paper on the biology of these parasites.

In the great majority of organisms, the reproducing individual does not engender all of its progeny simultaneously. Between the beginning and the end of the reproductive period there is usually a certain interval of time, during which the production of offspring continues in a manner depending, on the one hand, upon the specific characteristics of the organism, and on the other, upon the conditions under which it lives. From this simple fact follow some interesting consequences.

If the successive generations are separated by a long interval of time and conditions during this interval are of such a nature that the organism is inactive and in the condition of obligatory dormancy, known as diapause, then, in spite of the increase of the population, the generations will remain separate and distinct, and a comparison of the total populations in the successive reproductive periods will enable us to determine the rate of increase.

On the other hand, if the interval between generations is short and favourable to activity and the organism does not pass through a period of obligatory dormancy at this time, then, as the species increases, the successive generations will come to overlap, and the amount of overlapping will increase progressively as time goes on.

This is primarily due to the fact that when there is reproduction over a period of time-intervals, in a typical individual of the species, and conditions remain constant then the number of time-intervals during which births occur will increase from generation to generation.

The following notes are based almost entirely upon actual rearing records, the hosts in most cases being insects of economic importance. The greatest attention has been paid to parasites of the small moth-borers of sugar-cane (Diatraea spp.). The systematic work has been done entirely at the British Museum and would have been impossible without the facilities in literature and collections there, and the great help of Mr. D. S. Wilkinson and Dr. C. Ferrière, of the Imperial Institute of Entomology. Types of new species are in the British Museum.

Acroclisoides indicus, sp. n. (fig. l).

♂. Head and thorax dark metallic green ; abdomen with bluish reflections ; the short petiole black, the 2nd segment brown or more or less yellow. Antennae brown, scape and pedicel yellow. Mandibles yellowish with dark teeth. Tegulae and legs yellow, only the anterior and posterior coxae (except tip of posterior) green.

In order to follow the changes appertaining to the post-embryonic development of the larva of the Indian lac-insect of the genus Laccifer a knowledge of its external

and internal anatomy was a desideratum. A study of its external and internal anatomy was, therefore, undertaken in order to obtain a knowledge of its organography, and the following account is based on the results of such a study.

When teaching Entomology under University conditions, it is difficult to avoid giving students the impression that the principal, and perhaps the only, function of an entomologist is the examination of insect-corpses in great detail. Some years ago, when appointed lecturer on Entomology at the University of Sydney, I was faced with the problem of how to deal with this difficulty. Eventually I came to the conclusion that the only satisfactory solution of the problem was to obtain photographs of living insects with which to illustrate lectures, for it is almost impossible to arrange for students actually to handle more than a very small number of living insects. As the number of suitable photographs which have been published is small and quite inadequate for lecturing purposes, I found it necessary to take the photographs myself.