Siphuncular structure in the orders Tarphycerida and Barrandeocerida (Cephalopoda: Nautiloidea)

Abstract: The siphuncular structure is described in two Silurian taxa, Boionautilus tyrannus and Cumingsoceras complanatus, currently placed in the Tarpycerida. Tarphycerids have the Nautilus type of connecting ring that is composed of an outer, thick, spherulitic‐prismatic layer and an inner glycoprotein layer, the latter was destroyed by diagenesis. However, both Silurian specimens have the connecting ring of the calcified‐perforate type, previously known to occur in orthocerids, actinocerids, plectronocerids and now also in barrandeocerids. In this type, the inner layer of the connecting ring is calcified and perforated by pore canals. Boionautilus and Cumingsoceras are therefore classified with barrandeocerids and not with tarphycerids.     

SIPHUNCULAR STRUCTURE IN SOME FOSSIL COLEOIDS AND RECENT SPIRULA

Abstract: In Jurassic Phragmoteuthis huxleyi Donovan (Order Phragmoteuthida) the siphuncular wall shows unique structural and morphological features. The septal neck is short, about one‐eighth of chamber length, but the connecting ring is extremely long, extending through 5–6 chambers. The permeable siphuncular wall in each chamber is, therefore, unusually thick and consists of 5–6 consecutive connecting rings. Each connecting ring is calcified and has a highly porous structure in being composed of bundles of spicular crystallites, orientated more or less at right angles to the siphuncular wall, and separated by smaller or larger interspaces. A restudy of the belemnoid Megateuthis gigantea (Schlotheim) and the aulacoceratid Mojsisovicsteuthis? shows that the connecting rings in these taxa are also calcified. Each ring has a length of two chambers and consists of several calcified lamellae that are traversed by minute pores. The permeable siphuncular wall in each chamber therefore consists of two consecutive connecting rings separated by a porous prismatic layer. In Recent Spirula the connecting ring is composed of two layers: an outer spherulitic‐prismatic layer and an inner glycoprotein layer, of which the latter is not preserved in dry shells. The connecting ring structure is here similar to that in Recent Nautilus. Our study shows that at least three different structural types of siphuncular wall occur in coleoids. The phragmoteuthid connecting ring has a primitive structure, unknown in other cephalopods. This indicates that this taxon has no closer relationship with other coleoid taxa. The belemnitid‐aulacoceratid connecting ring is calcified and traversed by numerous pore canals. It shows a certain structural similarity to that in fossil actinoceratid and orthoceratid nautiloids. The spirulid connecting ring is structurally similar to that in Recent Nautilus and fossil nautilitid and tarphyceratid nautiloids. Thus the connecting ring structure indicates that coleoids include several, phylogenetically clearly separated lineages.     

LATE CAMBRIAN PLECTRONOCERID NAUTILOIDS AND THEIR ROLE IN CEPHALOPOD EVOLUTION

Abstract:  Numerous plectronocerid nautiloids appear in the Upper Cambrian of China. We have restudied their siphuncular structure, first described some 20 years ago. The siphuncle is characterized by: (1) long and holochoanitic septal necks dorsally but short and recurved necks laterally and ventrally; (2) strongly expanded connecting rings laterally; (3) two calcified layers in each connecting ring, outer spherulitic-prismatic and inner compact, the latter perforated by numerous pore canals; and (4) highly oblique siphuncular segments. The strongly expanded lateral sides of the connecting rings, together with the highly oblique course of the siphuncular segments, considerably enlarged the surface area of the connecting rings in each chamber, thereby increasing the transport capacity of cameral liquid. Thus, from their first appearance, plectronocerid nautiloids had developed a siphuncle for the replacement of cameral liquid with gases, and this system had a better and a more sophisticated design than that seen in stratigraphically younger nautiloids. However, their small orthoconic or slightly cyrtoconic shells were not well adapted for jet-powered swimming.     

CONTROL OF THE EUROPEAN RABBIT (ORYCTOLAGUS C. CUNICULUS L.) AN EXPERIMENT TO COMPARE THE EFFICIENCY OF GIN TRAPPING, FERRETING AND CYANIDE GASSING

Two similar adjacent areas of grass-heath were enclosed by rabbit-proof netting and the bulk of the rabbits on one area removed by gin trapping (in the holes) and on the other by ferreting. Trapping was followed by pump gassing and ferreting in its turn by spoon gassing, with a cyanogenetic powder.
Gin trapping yielded a higher return of rabbits per man hour (1.5) than ferreting (1.0), particularly during the initial stages of clearance. Ferreting gave a steady return.
Pump gassing of burrows, when surface-living rabbits were present, proved ineffective, owing to re-opening of holes from the outside.
Spoon gassing of burrows, integrated with the removal of surface-living rabbits by 'dog and gun', was successful but expensive in time (0.5 rabbits per man hour), compared with gin trapping and ferreting.
The valuable place of 'dog and gun' in planned rabbit clearance was clearly demonstrated.
Trapping yielded equal numbers of bucks and does. Ferreting yielded a higher proportion of does. Spoon gassing (after ferreting) yielded more bucks than does when the holes were dug out. Surface-living rabbits were predominantly bucks.     

Detection of Differences in Surface-charge-associated Properties of Cells by Partition in Two-polymer Aqueous Phase Systems

WHEN aqueous solutions of two polymers are mixed in certain proportions they may form two-phase systems^1,2 which can be buffered and used to partition and separate cells, particles and macromolecules by countercurrent distribution (CCD). Partition generally depends on polymer composition and concentration, the ionic composition and the charge sign of the material being partitioned. Such systems have been used to separate erythrocytes from white cells and erythrocytes on the basis of age. Changes in the surface properties of cells resulting from enzyme treatment or storage have also been demonstrated by this means³. Higher cell partition often accompanies increasing electrophoretic mobility which suggests that surface charge may be an important factor in partitioning^4–6. An apparent exception to this is the increased partition of stored human erythrocytes as compared with fresh⁷, as opposed to the mean electrophoretic mobility of both cell populations which remain identical⁸.     

Models of the Use of Root-zone CO2 by Selected North American Isoetids

Sediment CO₂, entering via the roots, contributes a significantportion of the total carbon uptake for isoetids (small, evergreen,submersed, vascular plants). Laboratory studies of inorganiccarbon uptake via the roots and shoots by five isoetids wereused to model the use of root-zone CO₂. Simple first-order linearmodels accounted for at least 75 per cent of the variation inthe data for Gratiola aurea, Isoetes macrospora, Littorellauniflora and Lobelia dortmanna. For Eriocaulon septangulare,which relies almost exclusively on root-zone CO₂, models couldaccount for only about 62 per cent of the variation in root-zoneCO₂ use. For each species, we present the best fitting regressionof root-zone CO₂ use as a function of root- and shoot-zone CO₂concentrations. For the species studied, carbon uptake was not saturated atfield concentrations of root and shoot-zone CO₂. Maximum ratesof carbon uptake were lower for species that naturally occurredat greater depths, compared with species more common in shallowwater. At equal external CO₂ concentrations carbon entry perunit root surface area was several times more rapid than entryper unit shoot surface area for L. dortmanna. The entry ratesper unit root and shoot surface area were about equal for G.aurea and E. septangulare. Shoots were equally or more permeablethan the roots of L. uniflora and I. macrospora, a fact thatmay be related to the functioning of crassulacean acid metabolismin these plants. Carbon, CO₂, photosynthesis, isoetid, Eriocaulon septangulare, Gratiola aurea, Isoetes macrospora, Littorella uniflora, Lobelia dortmanna     

Ultrastructural Characteristics of the Nacre in Some Gastropods

The nacreous layer in Gibbula, Calliostoma, Trochus and Haliotis is described on the basis of scanning electron microscopic studies. The central part of each nacreous tablet contains a significant amount of calcified organic matrix which is insoluble in a chromium sulphate and a 25% glutaraldehyde solution. In most cases, the tablet is subdivided by radial vertical organic membranes into a varying number (2 to 50) of crystalline sectors. These sectors represent polysynthetically twinned crystal individuals which form cyclic or interpenetrant twins. The nacreous tablets in gastropods are compared with those in bivalves, and with the non-biogenic aragonite. The mechanical properties of the nacre, and the effects of the interlamellar conchiolin membranes upon the nucleation of the tablets, are discussed.     

Sporozoites of Mammalian Malaria: Attachment To, Interiorization and Fate Within Macrophages

Sporozoites of Plasmodium berghei and Plasmodium knowlesi, incubated in normal serum readily interact with peritoneal macrophages of mice or rhesus monkeys, respectively. Interiorization of the sporozoite requires that both serum and macrophages be obtained from an animal susceptible to infection by the malaria parasite. Serum requirements for sporozoite attachment to the macrophage are less specific. Phagocytosis is not essential for the parasites to become intracellular. Our findings indicate that active penetration of the sporozoites into the macrophages does occur.     

The Effect of a Eugregarine Gregarina polymorpha (Hammerschmidt) on the Mealworm Larva of Tenebrio molitor (L.)

SYNOPSIS. The larva of the beetle Tenebrio molitor (Coleoptera, Tenebrionidae), commonly referred to as the mealworm, harbors considerable numbers of gregarines in its midgut. These are not necessary for normal growth, nor do they prolong the life of larvae grown under optimal conditions of temperature, relative humidity and diet. When the larvae were grown under optimal conditions there was no significant difference between the length of larval life or the final pupal weight of mealworms harboring gregarines when compared with mealworms which had been reared free from gregarines. This applied both to infected and non-infected larvae grown singly and in communal cultures.
When, however, larvae were grown on a sub-optimal diet, the gregarines had a considerable effect on the final pupal weight and the ability of the larva to complete development.