Apical Groove Research Articles

Stone City and Cook Mountain (Middle Eocene) Scaphopods from Southeast Texas: ABSTRACT

Middle Eocene exposures on the Brazos and Little Brazos Rivers yield numerous specimens of a wide variety of fossils, especially mollusks. Although this fauna has been known to paleontologists for many years, relatively few of the fossil groups have received a detailed analysis. Eighteen species of scaphopods have been found in the Stone City and Cook Mountain (Claibornian) Formations of the Brazos River valley. These include 11 species of Cadulus, 4 of Dentalium, and 3 of Fustiaria. Of these, 10 species are new. Apical fragments show that some scaphopods truncate their apexes by periodically discarding a significant portion of the test. By some mechanism or process, probably absorption, shell material is removed at a distance from the apex. The configuration of this shell removal is such that apical slits or grooves are already formed when truncation occurs. After truncation a pipe or sheath, which extends from the orifice of the truncated apex, may develop. End_of_Article - Last_Page 1832------------

Histological studies on the genus Fucus. IV. Regeneration and adventive embryony

Regeneration in Fucus vesiculosus L., both under natural conditions and in culture, has been studied histologically.Cut segments of vegetative tissue from mature Fucus specimens were cultured in seawater. Histological sections of this material were prepared at various intervals up to 8 months of culture to follow the development of adventitious branches from the wound surfaces. In both cultured segments and whole, naturally wounded plants, existing filament and cortical cells in the midrib region of wound surfaces differentiate a new epidermis. Several loci on this new epidermis undergo increased rates of periclinal division to produce structures which are morphologically very similar to normal Fucus embryos and which ultimately acquire apical grooves and apical cells and become flattened in the manner of normal vegetative thallus branches. The significance of the wound-healing process and the formation of adventive embryos is discussed.

The Status and Affinities of Duvaliopsis Jeannel (Coleoptera: Carabidae)

The genus Duvaliopsis was established by Jeannel (I928) for a small group o.f endogeno.us, ano,phthalmous trechines trom the Carpathian Mountains and the Transylvanian Alps ,o.f Romania, Czechoslovakia, and Poland. Although earlier authors had classified them with Anophthalm,us Sturm, Trechus Clairville, or Duvalius Delarouz6e (formerly considered a subgenus of Trechus), Jeannel (1928) clearly demonstrated their morphological similarity to Trechoblemus Ganglbauer and to North American cavernicole trechines of the genera Pse.udanophthalmus and Neaphaenops. Duvaliopsis, Pseudanophthalmus, and Neaphaenops were placed in a s6rie phyl6tique de Trechoblemus, united by the common possession o.f certain .characters (I) the mentum is fused to. the prementum; (2) the recurrent portion of the apical groove o.f the elytro.n is usually .connected to or directed t,o.ward the 3rd longitudinal stria; (3) the copulatory sclerites (o.f which there are one or two) are placed laterally (anisotopic), rather than ventrally (isotopic), in the internal sac; and (4) the anterior tibiae are pubescent on the ,outer side. Subsequent to I928, additional genera in North America and Japan have been described which sho.uld probably be allied with this. series (Valentine 1952, Yoshida and Namura 19.52, U6no 1956 and 1958, Barr I96O). In the eastern United States, the largest and most widely distributed genus of cave beetles is Pseudanophthalmus, species .o.f which are no.w known from Indiana, Kentucky, Tennessee, Alabama, Georgia, Ohio, Virginia, West Virginia, and Pennsylvania. Although found only in caves up to the present time, a few Virginia species have rudimentary eyespots, suggesting comparative recency of adopting a wholly subterranean mode of life. The absence of epigean trechines from North America which seem to share a relatively recent ancestry with Pse.udanoDhthalmus and other cave genera has provoked considerable speculation on the history and evolution of the, group. Trechofdes fasciatus Mo.tschulsky, from the Oligocene Baltic amber, could belong either to Lasiotrech,us or Trechoblemus (Jeannel, 928). This fossil demon

Chromosomes and chromocentres in the nuclei of Halidrys siliquosa (L.) Lyngb.

DIVIDING nuclei in the apical groove of Halidrys siliquosa show large numbers of small chromosomes, and at metaphase more than 55 have been counted (Fig. 1c, d, e). Metaphase plates at the first three divisions in developing antheridia have given counts of the order of 30 chromosomes (Fig. 1b), and one at the first division of the oogonium of approximately 28 chromosomes. This indicates that the thallus of H. siliquosa is diploid with meiosis at the first division of the gametangia, as is usual in the Fucales1.

Cytological studies of sterile bulls with spermhead abnormality

Cytological stvidies did not show any detectable structural changes which could be related to the spermhead deformity in a series of sterile bulls described by Hancock. The deformity according to Hancock consists of a deeply stained (in iron haematoxylin) area placed askew at the apex of the spermhead.In spermateleosis it is connected with persistence of the shallow apical groove of the nuclear membrane observed only in earlier stages of development in normal cases. There is also a formation of vacuoles in the developing spermheads in the region of the apex and of the equatorial belt. The apex of the abnormal spermhead treated with Feulgen reagent appears to be cut off askew.Formation of vacuoles in the developing spermheads may be related to some unknown changes in the nucleic acid metabolism of the spermhead. The absence of any chromosomal aberration, whether of quantitative or structural nature, may lead to the conclusion that the changes observed are due to a gene mutation.

Causes of Periapical Infection

The aim of the present study was to compare sonic activation using EDDY (VDW, Munich, Germany), passive ultrasonic irrigation (PUI), and mechanical activation using the XPendo Finisher (FKG Dentaire, La Chaux-des-Fonds, Switzerland) for the removal of calcium hydroxide from artificial grooves in straight root canals.The root canals of 90 human maxillary incisors with straight root canals were prepared using Mtwo files (VDW) up to size 40/.04, and the teeth were split longitudinally. A lateral groove in the apical or coronal part was prepared in each root half and filled with calcium hydroxide, and the root halves were reassembled. Five groups were established according to the removal techniques: group A, the XPendo Finisher; group B, EDDY; group C, PUI; group D, manual irrigation with a syringe; and group E, no irrigation (the control group). The activation procedures were performed for 30 seconds with 3 mL sodium hypochlorite 3% as the irrigant. The cleanliness of the grooves was scored under 10× magnification. The median of scoring was analyzed using the Kruskal-Wallis test (P = .05).All activation techniques were significantly more effective in the removal of calcium hydroxide than manual irrigation (P < .05). Regarding the apical groove, EDDY and PUI were significantly more effective in the removal of calcium hydroxide than the XPendo Finisher (P < .05). No difference was found for the coronal groove (P > .05).EDDY and PUI were significantly more effective in the removal of calcium hydroxide than the XPendo Finisher regarding the apical region. Manual irrigation was significantly less effective than all activation techniques.