Observations on the ultrastructure of the flagella and periplast in the Cryptophyceae

The flagella in Cryptomonas ovata Ehrenberg and two other un-named strains of Cryptomonas both bear stiff hairs with fine distal filaments of the same type as those found in the Xanthophyceae, the Chrysophyceae sensu stricto, the Phaeophyceae, the Bacillariophyceae, the Eustigmatophyceae and the Oomycetes. On the longer of the two flagella the hairs are 2·5 µm long and in two opposite rows whereas on the shorter flagellum they measure only 1 µm, are arranged in a single row and are more closely spaced. The long flagellum also bears a characteristic lateral swelling with a tuft of hairs of the same type as on the remainder of the flagellum, at approximately the level at which it emerges from the gullet. The hairs on the flagella of Hemiselmis rufescens Parke are distributed in a similar manner to those in Cryptomonas but they are more flexible and the swelling and tuft of hairs appear to be absent from the long flagellum. Hairs are apparently absent from the short flagellum of Chroomonas sp. The periplast in Cryptomonas ovata shows a hexagonal pattern in surface view and in sections of all three Cryptomonas strains appears as a typical plasmalemma underlain by a discontinuous layer of electron-dense material with variable substructure. The distribution of flagellar hairs and the structure of the periplast appear to be characters unique to the Cryptophyceae and these features emphasise the isolated position of this class of algae.     

Taxonomic notes on some freshwater planktonic Cryptophyceae based on light microscopy

The cryptomonads sampled frequently from pelagial of large freshwater bodies, lakes and ponds, but also found in littoral regions and in small water bodies covered with vegetation, are often characterized by the sigmoid (S-shaped) form of their cells. According to the quoted findings of electron microscopy it seems that these species should be incorporated into the new genus Campylomonas Hill. Because the EM characteristics have not been proved so far for all species, and the following nomenclatural combinations accomplished, the traditional classification into the genus Cryptomonas is kept here. The correct name for the largest of sigmoid cryptomonads is Cryptomonas curvataEhr. em. Penard. Contrarily, C. rostrata Troitz. em. Kisel. is to be held for later synonyms. The existence of the species C. rostratiformis Skuja remains uncertain. The smaller species of sigmoid shape, i.e. C. reflexa (Marss.) Skuja and C. marssonii Skuja, may also easily be discerned under the light microscope. From the small puddles with H₂S in water, shortened forms of both these species are documented, one of them under the published name C. anas Javorn. The pelagic assemblage of the above sigmoid cryptomonads frequently is completed by Plagioselmis nannoplanctica (Skuja) Novar., Lucas et Morr. and by P. lacustris (Pasch. et Ruttn.) Javorn. These flagellates so far are currently determined as the species of the genus RhodomonasKarsten. In addition to the EM characteristic, they differ from Rhodomonas by the absence of a true gullet (pseudopharynx) having only the ventral furrow with rows of superficial ejectosomes (similar to the genus Cryptochrysis Pascher). The ellipsoidal or ovoid cryptomonads are sampled more frequently from peat pools and small water bodies covered with vegetation than from open pelagial of lakes. An erroneous determination of them causes confusion. Because some strains are wrongly labeled, electron-microscopic characteristics are vaguely determined species. For example, some EM features of Cryptomonas ovata in fact belong to C. pyrenoidifera Geitl. or to C. phaseolus Skuja. Cryptomonas ovata Ehr. em. Stein is not a collective species with a wide dimensional range of ellipsoid cells. It is a large species the typical morphology which is described here in detail. C. splendida Czosn. differs from C. ovata only by the transversal orientation of the cell. Similar to C. ovata but smaller species is C. tatrica Czosn. These species are further compared with the well-defined species C. obovata Skuja and the particularly small C. phaseolus Skuja.     

Observations on the ultrastructure of representatives of the genera Hemiselmis and Chroomonas (Cryptophyceae)

Hemiselmis rufescens Parke and three species of the genus Chroomonas have been examined by electron microscopy. They demonstrate certain characteristic features of the Cryptophyceae, such as the presence of trichocysts and the arrangement of thylakoids in pairs in the plastid. The prominent pyrenoid of the genus Chroomonas is penetrated longitudinally by a tongue of cytoplasmic matrix which originates from between the two pairs of plastid membranes. In the genus Hemiselmis, however, the pyrenoid is traversed by a pair of thylakoids. The nucleus, Golgi apparatus and Corps de Maupas also occupy characteristic positions. These features indicate a close relationship between these two genera and the other major genus Cryptomonas, and support the suggestion that the Cryptophyceae is a discrete taxonomic group.     

Fluorescence lifetime and quenching studies on some interesting diphenylhexatriene membrane probes

The fluorescence lifetimes of a number of membrane probes based on the 1,6-diphenylhexatriene (DPH) chromophore have been measured in small unilamellar phospholipid vesicles and found to be multiphasic. These probes were quenched by sodium iodide with different efficiencies in vesicles and this has been attributed to the depth of the particular probe in the bilayer. The distribution of the probe between the outer and inner monolayer has been determined for those probes with fixed positions in the bilayer. The iodide ion permeability of the bilayer was found to be immeasurably small over a 3 h period.     

Observations on some Bohemian and foreign cheirurid trilobites

Some new taxa of cheirurid trilobites are described from the Lower Palaeozoic of Bohemia and Portugal (see the names in the introduction). The cephala and pygidia of the species C. (Crotalocephalina)gibba gibba, C. (C.)globifrons and C. (C.)pauper have been determined. The speciesEccoptochiloides tumescens andE. scuticauda have been proved to be conspecific.     

Epigenetics and phenotypic variability: some interesting insights from birds

Little is known about epigenetic mechanisms in birds with the exception of the phenomenon of dosage compensation of sex chromosomes, although such mechanisms could be involved in the phenotypic variability of birds, as in several livestock species. This paper reviews the literature on epigenetic mechanisms that could contribute significantly to trait variability in birds, and compares the results to the existing knowledge of epigenetic mechanisms in mammals. The main issues addressed in this paper are: (1) Does genomic imprinting exist in birds? (2) How does the embryonic environment influence the adult phenotype in avian species? (3) Does the embryonic environment have an impact on phenotypic variability across several successive generations? The potential for epigenetic studies to improve the performance of individual animals through the implementation of limited changes in breeding conditions or the addition of new parameters in selection models is still an open question.     

Field Observations on some Northern Nigerian Birds

T hese observations were made during a fifteen months' tour in Nigeria. From May 1937 till February 1938 the writer was stationed at Kafanchan, 9° 40' N., 8° 20' E., in Plateau Province, with a touring area which included the Jemaa and Southern Divisions of Plateau Province and the Nasarawa Division of BenueProvince; thereafter from March till August he was engaged on sleeping sickness work, which involved extensive travelling in Plateau, Benue, and Niger Provinces.