A Century of Sea Urchin Development

SYNOPSIS. In the last quarter of the nineteenth century severalinvestigators including Richard and Oskar Hertwig, Theodor Boveri,Hans Driesch, Curt Herbst, T. H. Morgan and others turned theirattention to sea urchin eggs and early embryos. This favorablecombination of outstanding investigators and the sea urchinembryo as an experimental organism contributed to a fundamentalunderstanding of the cell, fertilization and heredity. The advantagesof the sea urchin continued to be recognized as experimentalembryologists used these embryos to develop the concepts ofgradients, regulative development and inductive interactions.Then, as developmental biology arose from chemical embryology,the sea urchin embryo once again emerged as an ideal experimentalanimal, pivotal in the understanding of the molecular and developmentalbiology of eukaryotic organisms.     

Predispersal seed predation in native leguminous shrubs and trees in savannas of southern Botswana

Seed predation by insects in the seed-crop of nine Acacia species, Dichrostachys cinerea , and Peltophorum africanum was examined in various tree savannas in Botswana. The degree of infestation varied strongly between and within species from 0% ( P. africanum ) to more than 80% ( A. hebeclada, D. cinerea ). Whereas in all Acacia species only one phytophagous hymenopteran ( Oedaule sp.) was present, the number of bruchid species varied between one ( Bruchidius sahlbergi on A. hebecluda, B. uberatus on A. nilotica ) and eight species ( Bruchidius div. spec., Caryedon sp., Spermophagus rufonotutus on A. tortilis ).
The life history of B. sahlbergi was studied in detail and lasted at least 100 days from egg to adult beetle. The life-span of adult beetles may extend to a further 57 days.

Résumé

Des observations ont été réalisées sur les dégâts d'insects dans les graines de neuf espèces d' Acacia , de Dichrostachys cinerea et de Peltophorum africanum dans les savanes arborées du Botswana. Le taux d'infestation varie fortement aussi bien entre les espèces que parmi les espèces de 0% ( P. africanum) à plus de 80% ( A. hebeclada, C. cinerea ). Alors que toutes les especes d' Acacia n'héberge qu'un seul Hyménoptère phytophage ( Oedaule sp.), le nombre d'espèces de Bruchidae observées varie de une ( Bruchidius sahlbergi sur A. hebeclada, B. uberatus sur A. nilotica) à huit ( Bruchidius div. spec., Caryedon sp., Spermophagus rufonotatus sur A. tortilis ).
Le cycle de développement de B. sahlbergi a étéétudié et dure au moins une certaine de jours. La longévité des adultes de cette espèce peut atteindre 57 jours.     

The Convergent Development of Orb-webs in Cribellate and Ecribellate Spiders

Orb-webs are highly developed and can be understood as the besttechnical solution of the problem how to place capture-threadsin the most efficient and economical way. They are built bycribellate and ecribellate spiders. Phylogenetical relationsbetween some families of Cribellate and Ecribellate cannot beignored, but for some important reasons it is difficult to imaginethat on the level of orb-weaving cribellate spiders became ecribellateby reducing the cribellum. Thus, these specialised webs musthave developed on both sides independently and are the resultof a convergent evolution. Steps leading from primitive useof threads for capturing insects to the typical and latter modifiedorb-webs of Cribellate and Ecribellate can be discerned.     

Computer-assisted visualization of the rat epididymis: a methodological study based on paraffin sections autometallographically stained for zinc ions

A concept for the computer-assisted visualization of tubular organs is presented. Unmarked histological zinc-stained serial sections from the epididymis of the Wistar rat were aligned to demonstrate the concept. Virtual images were made through the aligned sections and served as controls for the alignment process. Animation of the serial sections and the virtual images revealed new information about the structure of the organ under investigation. The analysis was used to upgrade the anatomical knowledge of rat epididymis by describing how the epididymal duct runs through the structure. The proximal parts of the epididymis contain large communicating septa of connective tissue dividing the caput and the upper part of the corpus epididymidis into segments. The tortuousness was high in the caput with many turns within a small area of the epididymis, whereas longer loops were found in the lower part of the corpus and cauda epididymidis. The tube of the vas deferens was found to become an integrated part of the ductal system in the cauda epididymidis, although it was histologically easy to distinguish from the epididymal duct. The total number of cross-sections of the ductus epididymidis in the 2254, 15-mu m-thick, tissue sections analysed was 104 700, giving a minimum length of the ductal system of 1.5 m. © 1998 Chapman & Hall     

Modulation of a Cell Surface Glycoprotein in Yeast: Acid Phosphatase

Upon inorganic phosphate starvation the cell wall glycoprotein acid phosphatase of yeast Saccharomyces cerevisiae is derepressed. Purified acid phosphatase isolated from early log phase cells differs in reactivity and stability from acid phosphatase from late log phase cells indicating that the two enzymes are structurally different. This demonstrates that the yeast cell has not only the capacity to regulate the amount of acid phosphatase but also the ability to vary (modulate) the structure of the secreted enzyme. Modulation of acid phosphatase may be a mechanism which is involved in morphogenetic and behavioral differentiation of the yeast cell.     

Role of Ethylene in Senescence of Petals--Morphological and Taxonomical Relationships

Petal senescence in mature flowers was studied in 93 speciesfrom 22 families. The initial symptom of senescence was eitherwilting or abscission, but in some species the time span betweenwilting and abscission was very short. There was no apparent relationship between corolla form (choripetalousor sympetalous), ovary position (inferior or superior with respectto the corolla) and type of senescence (initial wilting or initialabscission). In monocots no initial abscission was found, whilein dicots the difference between the wilting type and the abscissiontype was generally at the family level. With respect to petalsenescence, sensitivity to exogenous ethylene (C₂H₄) was alsorelated to the family level. Except for a few families (all tested Campanulaceae, Caryophyllaceaeand Malvaceae, and most Orchidaceae), most of the flowers investigatedthat showed initial wilting were not sensitive to exogenousethylene, e.g. all tested Compositae, Iridaceae, and Liliaceae.Most of the flowers showing initial abscission were sensitiveto exogenous ethylene (Geraniaceae, Labiatae, Ranunculaceae,Rosaceae, Scrophulariaceae). Experiments with silver thiosulphate (STS) confirmed the effectsof exogenous ethylene, both in flowers showing initial wiltingand in flowers showing initial abscission. The data indicate,therefore, that ethylene is involved in the natural senescenceof only a minority of the wilting type of flowers and in a majority(if not all) of the abscising type of flowers. Key words: Abscission, ethylene, senescence, silver thiosulphate