Slender Thread Research Articles

DISTRIBUTION OF PROTEIN-BOUND SULFHYDRYL GROUPS IN YEAST CELLS

Young and old cultures of 12 yeasts have been stained by the Barrnett-Seligman histochemical procedure for localization of sulfhydryl groups. Thiol groups have been found distributed in the cytoplasm, but not in the cell wall. The intense staining of sulfhydryl groups by the specific stain was clearly showns in the slender thread of protoplasm between bud and mother cell. The intensity of staining in the proliferating cell was higher than in the resting cell; variations in thiol content between various yeast species were recorded. No decrease in thiol content of yeast spores, as compared with vegetative cells, has been found in Schizosaccharomyces octosporus, whereas the staining of yeast spores in Saccharomyces and Hansenula was found to be negligible. Implications of these findings are discussed.

Spermatogenesis of a cestode.

THE interpretation of the structure of the spermatozoa of cestodes and of the process of spermatogenesis is subject to wide divergence of opinion. In 1935 Young1 directed attention to the lack of knowledge regarding cestode structure and development, and among the main problems awaiting solution discussed the method of cell division and the structure of the sperm. Regarding the latter he wrote that “we have even less information than we have about most cestode tissues and until the spermatogenesis is known this ignorance will continue”. His observations2,3 and those of Child4 “suggest a very simplified structure correlated with rapidity of development and the production of enormous numbers of spermatozoa”1. Watson5 believed that the spermatozoon of Gyrocotyle is provided with a head. He did not, however, make a detailed study of spermatogenesis and described the sperm as “a slender thread tapering at the posterior end, with a well marked head, several times the diameter of the body”. In a description of a figure of two spermatozoa he mentioned head, tail and acrosome. Presumably the acrosome is a short threadlike structure figured at the anterior end of the head. Since the publication of Young's paper1 no further information on the spermatogenesis of cestodes has become available.

The developmental history ofMutela bourguignati(Ancey) Bourguignat (Mollusca: Bivalvia)

An account is given for the first time of the development ofMutela bourguignati(Ancey) Bourguignat, an African freshwater bivalve of the family Mutelidae. Eggs are shed in large numbers into the inner demibranchs. There they develop into minute larvae similar in some respects to the lasidium larvae of certain South American freshwater mussels, but differing in several ways. Each larva consists of a rounded body covered dorsally and laterally by a thin pellicle and provided anteriorly with two lobes clothed with cilia. Posteriorly, and on the ventral surface, are two sets of minute hooks. Anteriorly is a remarkable elongate, flaccid and colourless tentacle more than seventy times as long as the larva itself. There is no gut, nor can endodermal or mesodermal tissues be recognized as such at this stage. After liberation via the exhalant siphon these larvae settle on the cyprinid fishBarbus altianalisradcliffiand there metamorphose and begin a parasitic phase of development. The larval pellicle folds, and its opposed edges fuse so as completely to enclose the larva. Two tubular outgrowths grow from its anterior end into the superficial tissues of the fish and serve both as organs of attachment and nutrition. In their vicinity skeletal tissues of the host are broken down. The main body of the larva, now designated the haustorial larva, elongates and becomes differentiated into a stalk and a bud. The stalk protrudes from the fish and bears the bud clear of the host. Within the bud the adult bivalve eventually develops. The stalk is traversed by long prolongations of the mantle which run into the haustorial tubes and function as absorptive tissues. The cuticle is not calcified nor is it composed of conchiolin. As differentiation proceeds the definitive mantle, which is the lineal descendant of the larval mantle, begins to secrete first periostracum then calcareous matter to form the rudiments of the valves, and a rudiment of the ligament is also formed. As adult features gradually appear the bud is burst and a young bivalve, little more than 1 mm in length, attached to a long stalk emerges. Independent, particulate feeding commences at this stage. Rupture of both cuticular and mantle elements eventually takes place at the point of juncture of stalk and young bivalve and the latter falls away to begin an independent existence. At the time of release it is capable of active locomotion and is able to produce a slender byssus thread. A detailed, illustrated account of these changes, both external and internal, is given, and the development of certain individual organs is traced. The nature of the cuticle of the haustorial larva, the effect of this larva on its host, and the affinities and probable evolution of the larval stages are discussed, and the importance of taking larval development into account in classification is emphasized.

Electron Optical Observations on Chromosome Structure in Resting Cells

PRESENT knowledge of chromosome structure is based chiefly on observations made on fixed preparations of large mitotic chromosomes or of the so-called giant chromosomes in the salivary gland of certain diptera with microscopes utilizing visible or ultra-violet light1. A preliminary account has recently been published of electron microscope studies on large plant chromosomes2. Little or nothing is known concerning the structure of chromosomes in resting cells beyond the fact that they are present in the form of exceedingly slender threads (chromonemata) or of the so-called chromatin network3.

Tacitus and Agricola

BUT for Tacitus' biography, Agricola and his governorship of Britain would be almost unknown to us. A piece of lead pipe at Chester,' and passing references in Dio Cassius2 would be the sole evidence for the fame and activity of perhaps the greatest governor the province ever had. Tacitus has indeed succeeded in his self-appointed project of preserving the memory of his father-in-law for the admiration and profit of future ages. This curiously slender thread of transmission has been emphasized often enough before,3 but it now seems that Agricola has survived the perils of the Dark Ages only to meet with worse. Having become one of the most widely known and, with a monograph to himself, best attested of Imperial personalities, modern criticism has subjected him to a new danger, a danger not of oblivion but of discredit. He is involved in the scepticism with which Tacitus' value as a historian has been viewed: the characterizations in the pages of Tacitus, when checked with independent evidence, are not infrequently shown to be misleading or coloured by bias. In particular, the reigns of Tiberius and Claudius now appear in a far better light through a more sceptical treatment of Tacitean evidence. And it is but a step for critics to consider the Agricola as similarly erroneous. Justification is not lacking. The monograph has been assailed as a whole and in detail, and has been no less vehemently defended.4 It has been suggested that it is as much a political pamphlet as a biography. Tacitus' animosity towards Domitian is well known, and the later chapters of the work must be taken with a pinch of salt on those grounds. The high principles of Agricola, whose worth Domitian failed to appreciate, and whose conquests he let slip, are written up ira et studio to damage Domitian's reputation yet further. Tacitus is said to be defending himself and other moderates like Agricola, who had acquiesced in the tyranny of Domitian's latter years. He argues that headstrong opposition and ambitiosa mors at such times are valueless as compared with the industria, vigor, obsequium, and modestia of men like Agricola, and that such men ought therefore not to be condemned in the wild reaction of the

Science since 1500

THIS book gives a very compact summary of the history of the chief sciences during the period indicated in the title, and also some retrospects covering earlier periods. The mode of presentation varies. Some of the chapters follow the main divisions of science, others confine themselves to some special problem, while others again are rather mixed bags the contents of which are strung together on somewhat slender threads.

Hurricane Modification of the Offshore Bar of Long Island, New York

N account of the New England hurricane of September 21, N 1938, and some of its effects has already been given in the Geographical Review.' It is the purpose of the present paper to report on a further aspect of the storm-the havoc wrought on the slender thread of sand constituting the offshore bar of southern Long Island. The damage to the bar was caused by huge storm waves striking from the crest of a swollen tide. Great gaps were opened in the bar, the high-water shore line was driven scores of feet inland, and acres of protective dunes were washed away. Many thousands of dollars have already been spent in reclamation work, and far larger sums will be involved if the comprehensive program of reconstruction now under consideration is adopted. The essential features of the proposed scheme are summarized on a later page. The present report not only describes the damage but attempts to analyze the processes involved. The post-hurricane modification of the bar, both natural and artificial, is considered, and the efficacy of the methods of artificial reclamation is examined. The changes effected in the bar may be summarized as follows: (1) formation of new inlets; (2) destruction of sand dunes; (3) development of shore-line irregularities; and (4) aggradation of the bar behind the dune line. In addition, the modification of the bar has so disturbed tidal conditions in the bays behind it that some areas formerly beyond the reach of even the highest tides are now periodically flooded.

Structure of Large Somatic Chromosomes

A number of years ago the writer published two papers (4I, 42) dealing respectively with the large somatic chromosomes of Vicia faba and Tradescantia virginiana. According to the descriptions given therein, the chromosome, apparently homogeneous in the anaphase, became visibly differentiated during the telophase into more chromatic and less chromatic constituents by a process which has previously been called "alveolation." The less chromatic constituent mingled with other fluids to form the karyolymph, not necessarily persisting as a portion of the individualized chromosome throughout the mitotic cycle. The more chromatic constituent of each chromosome constituted a portion of the metabolic reticulum, assumed the form of a slender thread in the ensuing prophase, underwent a longitudinal division, and then thickened and shortened to become the double metaphase chromosome. This chromatic constituent was held to persist throughout the nuclear cycle, assuming the form of a slender thread (chromonema) only during the early prophase, when its longitudinal division appeared to take place. Since that time certain other observers, notably MARTENS (23, 24), KAUFMANN (I2-14), and KUWADA (i6), have furnished cogent evidence in support of the view that in such chromosomes the two constituents mentioned are morphologically distinct and often

Mvlier aries, and Other Cruces in Catvllvs

This instalment of suggestions is put forward with all the diffidence one is bound to feel after an examination of the great body of the manuscripts. No great writer's text has hung upon a more slender thread of evidence. Larger matters than verbal emendation are touched upon in the discussion of poem LXVIII. My theory of how our texts became dislocated (and more than half of the extant manuscripts present an order quite different from that of GOR), and some new light I hope to throw upon the form and meaning of the Peleus and Thetis, must be withheld until a later occasion.

XIII. On gasterolichenes: a new type of the group lichenes

Until recently the time-honoured division of Thallogens into three primary groups, Algæ , Fungi , and Lichenes , was retained, the most prominent morphological features of the last group consisting in the vegetative portion being composed of slender achlorophyllose threads mixed with chlorophyll-producing cells or gonidia, and the spores produced in asci. It was assumed that the gonidia were in organic continuity with the colourless threads, an assumption challenged by Schwendener, who considers a lichen as a combination of a fungus and an alga, an idea now widely entertained, nevertheless, curiously enough, numbering amongst its opponents most of the leading lichenologists and mycologists of the day, most of whom, it is important to remember, are distinguished as systematists rather than as biologists. Later researches have placed almost beyond doubt the truth of Schwendener’s theory. Bornet has shown that in numerous instances the gonidia can with certainty be referred to some species of Algæ, and further succeeded in building up a lichen synthetically by sowing the spores of Parmelia parietina upon Protococcus . Stahl also, by growing the spores and gonidia ( pleurococcus ) of Endocarpon Pusillum , produced the lichen which bore perithecia and spermogonia. The same author has also demonstrated the presence of sexual organs of reproduction in a gelatinous lichen, Collema Microphyllum , the female portion resembling the carpogonium, with its trichogyne, met with in the Florideæ. Spermatia, produced in the spermogonia, are the fertilising elements. The discovery by Mattirolo of a second type of lichen structure, Hymenolichenes , characterised by having the spores borne on basidia, the latter compacted into a continuous hymenium as in Hymenomycetous fungi, has also considerably strengthened Schwendener’s theory, as the mutual relations between the two components can be more readily determined than in the older group of Ascolichenes .