BREEDING BIOLOGY OF THE MANX SHEARWATER PUFFINUS PUFFINUS

Studies on the breeding biology of Puffinus puffinus were carried out in 1963 and 1964 at the large colony on Skokholm, Wales. During the six weeks before laying the birds spent up to a quarter of the days in the burrows, but the ten days immediately prior to laying were normally spent at sea. There is a prolonged laying period, with a marked peak in the first half of May. Details are given of a second egg being laid when the first was deserted immediately after being laid. The male took the first incubation spell. The incubation spells ranged from one to 26 days and averaged six. The incubation period was about 51 days. The frequency of visits to land by breeding birds, unlike those by non-breeders, was not affected by the moon. On hatching, the chicks grew rapidly and reached maximum weights of between 505 and 755 gm. sometime between 39 and 61 days. There was a variable desertion period, usually eight or nine days, before the chicks left the island about 70 days after hatching. During the feeding period the chick received about two feeds every three days. There is evidence that adults visited the chicks more frequently than this. There was no correlation between growth of the chicks, their feeding rates or fledging weights and the time of laying. There was a high survival (about 95 %) of chicks during the fledging period but some eggs were lost in disputes for burrows. Nine pairs in 1964 were unable to raise two young simultaneously. Parents altered their feeding rhythms to try to feed two young but did not themselves lose weight. It is suggested that the critical factor in the production of young is the availability of food for the young immediately after they leave the colonies.     

武汉东湖轮虫种类组成及其分类讨论

作者根据Ｋｏｓｔｅ（１９７８）提出的轮虫分类系统对武汉东湖４个站１９９１年轮虫种类进行了分类。同时,对我国以往的轮虫分类中存在的若干问题进行了讨论。１９９１年作者共观察到轮虫６９种,隶属于１９个科,２９个属,新记录１２种,其中,采自水样的轮虫种类有５９种,沉积物中休卵萌发的种类４１种,两者相同种类３１种,休眠卵萌发特有种类１０种,其中的盘状鞍甲轮虫、侧刺伏嘉轮虫、侧扁棘管轮虫等在６０年代的东湖水体     

SOME THEORETICAL ASPECTS OF OSMIUM TETROXIDE FIXATION WITH SPECIAL REFERENCE TO THE METAPHASE CHROMOSOMES OF CELL CULTURES

Fixation of cell cultures with 1 per cent OsO₄ at constant pH and tonicity but variable cationic valence and dielectric constant causes profound changes in metaphase chromosomes. It is possible to make them disappear, flocculate, or show little change from the living cell in the phase contrast microscope. Conventional fixation for the electron microscope causes almost complete disappearance of metaphase chromosomes in phase contrast. Reasons for this behavior are discussed. It is postulated that intermolecular distances and consequently internal structure in chromosomes are governed by the same forces that govern these distances in colloidal sols.     

DEVELOPMENT OF SOME LAKE ECOSYSTEMS IN TROPICAL AFRICA, WITH SPECIAL REFERENCE TO THE INVERTEBRATES

1. The flooding of a lake basin initiates a series of changes leading eventually to a more stable climax situation after some years. Sequential physical and chemical changes in the mud and water and related changes in the animal and plant populations of three types of tropical African lakes are considered. The giant man-made lakes, Kariba and Volta, both several thousand square kilometres in area, provide the bulk of the material for this review. Two other kinds of tropical lake, the annual storage-reservoirs like Jebel Aulia and Sennar in the Sudan, and natural lakes subject to periodic droughts, like Lake Chilwa in Central Africa, are also considered. Evidence is often patchy but suggests a number of generalizations regarding the course and causes of the developmental changes in these tropical ecosystems. 2. On the evidence available, the course of development appears to fall conveniently into two periods based on water level changes, the filling phase and the post-filling phase. The former is characterized by sudden appearances of organisms and explosive growths of animal and plant populations. This unstable behaviour, especially characteristic of tropical lakes, is associated with the destruction of old habitats and the creation of new ones, the increasing area and volume of the new lake environment and the introduction of materials to the system at the advancing shore-line. By the time that filling is complete, the situation has stabilized to a large extent and the ecosystem enters a new phase. 3. This post-filling phase is characterized by the development and exploitation of existing habitats. Examples considered here are: the development of the mud habitat under the influence of processes like sedimentation and beach formation; the development of submerged woodland as a habitat for bottom dwelling animals; the spread of rooted aquatic plants and their effect on the mud; and the role of fluctuation in water-level on the post-filling phase. All four phenomena result in a modification of the substrata originally flooded, in a way that directly effects the associated fauna and flora. Apart from influencing the first three processes, water-level fluctuations also result in an interaction between the aquatic and terrestrial ecosystems which brings about important changes in itself. 4. The relative importance of these two phases varies with the type of lake, filling-phase phenomena obviously dominating in the annual storage reservoirs while post-filling phase characteristics are fully expressed in the large lakes made by man. 5. In contrast to the development of temperate lake ecosystems, succession of species in these tropical examples is not so much interrupted by major annual temperature changes. In addition, both the course of succession and the climax communities achieved are different. This may be largely due to the more rapid decomposition of organic matter in the muds which has two main consequences. In the first place, extraneous organic material brought in to the system during flooding, is rapidly broken down. Early filling stages, therefore, are associated with anoxic conditions and development of conspicuous communities of algae and large aquatic plants. The result is an overlapping of what in temperate systems are two distinct episodes: the early extraneous and later self-contained systems. Secondly, the replacement of chironomids by an oligochaete climax in the mud as seen in temperate lakes does not normally occur, apparently because of the lack of accumulated organic material. The presence in Africa of the may-fly Povilla adusta, on the other hand, provides an extra stage in the colonization of submerged woodland, replacing the earlier chironomid communities.     

THE TRANSMISSION OF PLANT VIRUSES BY BITING INSECTS, WITH PARTICULAR REFERENCE TO COWPEA MOSAIC

Experiments on the virus-vector relationship of the Trinidad cowpea mosaic virus, transmitted by Ceratoma ruficornis , gave the following results: ability to infect decreased with increasing time after ceasing to feed on infected plants, but vectors remained infective for 14 days (much longer than the longevity in vitro of the virus at glasshouse shade temperatures of 23–31°C.); the beetles transmitted more consistently after longer feeding on infected plants, though feeds of under 5 min. made them efficient vectors; the proportion of plants infected increased with the amount of feeding damage on them; fasting the vectors before feeding on infected plants increased voracity but had no effect on their ability to transmit; beetles became infective immediately after feeding on infected plants. Cowpeas were infected by inoculation with macerated infective vectors or with juice regurgitated by vectors. There is no evidence that aphids or other sucking insects can transmit the virus. It seems similar to squash mosaic and turnip yellow mosaic, for vectors of all three viruses probably transmit by regurgitating infective juice during feeding.