Apical Edges Research Articles

THE DYNAMICS OF WOUND CLOSURE AND ITS ROLE IN THE PROGRAMMING OF PLANARIAN REGENERATION. II - DISTALIZATION.

When the dorsal and ventral epidermal layers join by first intention during the closure of the wound, the cells of their borders (M-cells) do not meet in the same manner in all sections. In anterior sections the dorsal M-cells attach themselves to the ventral basement membrane, so that only the dorsal epidermis is stretched. In posterior sections the dorsal and the ventral M-cells join by their apical edges without being closely apposed to the wound surface. Only the ventral cells are stretched because of their specific motility. In longitudinal sections the dorsal and the ventral M-cells also join by their apical edges, but since they are closely apposed to the wound surface both epidermal layers are stretched. The stretching is a process equivalent to distalization. The junction between the dorsal and the ventral epidermis is shifted ventrally in the anterior wounds (as in the intact heads) and dorsally in the posterior wounds (as in the intact tails). Some abnormalities of wound closure have been observed at levels where heteromorphic regeneration frequently occurs. These findings are consistent with the hypothesis previously advanced (3) that the modalities of wound closure establish the programme for regeneration.

The crystal structure of tetra-arsenic trisulphide

The crystal structure of synthetic α-dimorphite, As4S3, has been determined by a three-dimensional single-crystal X-ray examination. The crystals, of space group Pnma, have Z= 4 in a unit cell of dimensions a= 9·12, b= 7·99, and c= 10·10 A. The structure was determined by application of Sayre's equation and electron-density methods, and refined anisotropically to R 0·11 for 575 observed reflections. The crystal consists of As4S3 molecules, of symmetry C3v, with four arsenic atoms in a triangular pyramidal arrangement and sulphur bridges along the three adjacent apical edges. Mean As–As and As–S distances are 2·45 and 2·21 A.

Development of the human fetal thyroid

The human fetal thyroid between the 65–80 mm crown-rump stage (73–80 gestational days) attains maturity in terms of relative weight, appearance of colloid containing central cavities, and ability to produce iodinated organic products, including thyroxine. The histogenesis of the central colloid cavities is brought about by the gradual enlargement and fusion of intracellular canaliculi. This mechanism is perhaps activated and controlled by the presence of increasing amounts of specialized cellular products, presumably thyroglobin. The strategic placement of desmosomes on the apical edges of the cells causes central containment of the individual disgorged canaliculi.

Morphology of the Temnopleuridæ

THE following is an abstract of a communication read before the Linnean Society, Dec. 15, 1881:—The Temnopleuridæ, a sub-family of oligopores, are remarkable for their sutural grooves and depressions at the angles of the plates. The author examined the grooves and depressions or pits in Saimacis sulcata, Agass, and found that these last are continued into the test as flask shaped cavities sometimes continuous at their bases which are close to the inside of the test, but do not perforate. This is the case in the median vertical sutures of the interradium and ambulacrum. Between the interradium and the poriferous plates of the ambulacra are numerous pits in vertical series which are the ends of cylinders closed and often curved within. Altogether the undermining is considerable. The grooves over the sutural margins are losses to the thickness of the test. The edges of the contiguous plates are sutured together, by a multitude of knobs and sockets 1/300 of an inch in diameter visible with a hand lens. In the vertical sutures there is an alternate development of knobs and sockets on each plate corresponding to a similar development on the opposed plates. Between the horizontal plate edges are sutures remarkable in their distinctness and position. The apical edges of the interradial plates have multitudes of sockets and the actinal edges, knobs: whilst the apical edges of the ambulacra! plates have knobs and the actinal have sockets. The ambulacra, on their interradial edge have nothing but knobs and the interradial plates corresponding sockets, so that a great series of knobs and socket “dowelling”prevails. Temnopleurus torematicus, Agass., gave similar results modified by the great development of the grooves and the young form was shown to differ from the adult, and to have rows of knobs and sockets, and barely penetrating pits. The arrangement in Salmacis bicolor and Amblypneustes ovum was considered. The pits have an importance for they increase the superficies of the derm and near the peristome, as indicated by Loven, they contain Sphœridia.