Placoid Scales on Sharks and Rays

Placoid Scales on Sharks and Rays Placoid scales are the tiny tough scales that cover the skin of sharks, rays, and other elasmobranchs. Even though placoid scales are similar to the scales of bony fish, they are modified teeth and are covered with hard enamel. They grow out of the dermis layer and this is why they are called dermal denticles. Placoid scales are packed tightly together, supported by spines, and grow with their tips facing backward. This gives the fishs skin a rough feel. The function of these scales is for protection against predators. In some sharks, they may also have a hydrodynamic function, helping them swim more efficiently and quietly. The placoid scales are shaped such that little vortices form, reducing friction as the shark swims. They also direct the water around the fish. The Structure of Placoid Scales The placoid scales grow out of the dermis, with the flat rectangular base plate embedded in the skin of the fish. Like our teeth, placoid scales have an inner core of pulp made up of connective tissues, blood vessels, and nerves. Like the pulp cavity of a tooth, it is nursed by a layer of odontoblast cells that secrete dentine. This hard, calcified material forms the next layer. The dentine is covered by enamel-like vitrodentine, which is produced by the ectoderm. Once the scale erupts through the epidermis, no more enamel can be deposited on that portion of the scale. Different species have different kinds of spines develop to support the scales. The spines give the scales their rough texture. It is so rough that it has been used as sandpaper by various cultures form many centuries. The species of fish can be identified by the shape of the scales and spines. On some sharks, they are shaped like a duck foot. Scales in bony fish grow as the fish gets larger, but placoid scales stop growing after they reach a certain size, and then more scales are added as the fish grows. Shark Skin Leather The tough nature of the placoid scales makes shark rawhide leather, called shagreen. The scales are ground down so the surface is rough with rounded protrusions. It can take on dye colors or be left white. It was used in Japan to cover sword hilts, where its rough nature was appreciated to help form a good grip. Other Types of Fish Scales Ctenoid scales are another kind of toothed scales, but the teeth are only along the outer edge of the scale. They are found on fish such as perch that have spiny fin rays. Cycloid scales have a smooth texture and they are found on fish with soft fin rays, including salmon and carp. They are rounded and show growth rings as they grow with the animal. Ganoid scales are diamond-shaped and they do not overlap, but they fit together like pieces of a jigsaw puzzle. They are seen on gars, bichirs, and reedfishes, and they act like armor plates.

Transformational Grammar (TG) Definition and Examples

Transformational Grammar (TG) Definition and Examples Transformational grammar is a theory of grammar that accounts for the constructions of a language by linguistic transformations and phrase structures. Also known as  transformational-generative grammar or T-G or TGG. Following the publication of Noam Chomskys book Syntactic Structures in 1957, transformational grammar dominated the field of linguistics for the next few decades. The era of Transformational-Generative Grammar, as it is called, signifies a sharp break with the linguistic tradition of the first half of the [twentieth] century both in Europe and America because, having as its principal objective the formulation of a finite set of basic and transformational rules that explain how the native speaker of a language can generate and comprehend all its possible grammatical sentences, it focuses mostly on syntax and not on phonology or morphology, as structuralism does (Encyclopedia of Linguistics,  2005). Observations The new linguistics, which began in 1957 with the publication of Noam Chomskys Syntactic Structures, deserves the label revolutionary. After 1957, the study of grammar would no longer be limited to what is said and how it is interpreted. In fact, the word grammar itself took on a new meaning. The new linguistics defined grammar as our innate, subconscious ability to generate language, an internal system of rules that constitutes our human language capacity. The goal of the new linguistics was to describe this internal grammar.Unlike the structuralists, whose goal was to examine the sentences we actually speak and to describe their systemic nature, the transformationalists wanted to unlock the secrets of language: to build a model of our internal rules, a model that would produce all of the grammatical- and no ungrammatical- sentences. (M. Kolln and R. Funk, Understanding English Grammar. Allyn and Bacon, 1998)[F]rom the word go, it has often been clear that Transformational Grammar w as the best available theory of language structure, while lacking any clear grasp of what distinctive claims the theory made about human language. (Geoffrey Sampson, Empirical Linguistics. Continuum, 2001) Surface Structures and Deep Structures When it comes to syntax, [Noam] Chomsky is famous for proposing that beneath every sentence in the mind of a speaker is an invisible, inaudible deep structure, the interface to the mental lexicon. The deep structure is converted by transformational rules into a surface structure that corresponds more closely to what is pronounced and heard. The rationale is that certain constructions, if they were listed in the mind as surface structures, would have to be multiplied out in thousands of redundant variations that would have to have been learned one by one, whereas if the constructions were listed as deep structures, they would be simple, few in number, and economically learned. (Steven Pinker, Words and Rules. Basic Books, 1999) Transformational Grammar and the Teaching of Writing Though it is certainly true, as many writers have pointed out, that sentence-combining exercises existed before the advent of transformational grammar, it should be evident that the transformational concept of embedding gave sentence combining a theoretical foundation upon which to build. By the time Chomsky and his followers moved away from this concept, sentence combining had enough momentum to sustain itself. (Ronald F. Lunsford, Modern Grammar and Basic Writers. Research in Basic Writing: A Bibliographic Sourcebook, ed. by Michael G. Moran and Martin J. Jacobi. Greenwood Press, 1990) The Transformation of Transformational Grammar Chomsky initially justified replacing phrase-structure grammar by arguing that it was awkward, complex, and incapable of providing adequate accounts of language. Transformational grammar offered a simple and elegant way to understand language, and it offered new insights into the underlying psychological mechanisms.As the grammar matured, however, it lost its simplicity and much of its elegance. In addition, transformational grammar has been plagued by Chomskys ambivalence and ambiguity regarding meaning. . . . Chomsky continued to tinker with transformational grammar, changing the theories and making it more abstract and in many respects more complex, until all but those with specialized training in linguistics were befuddled. . . .[T]he tinkering failed to solve most of the problems because Chomsky refused to abandon the idea of deep structure, which is at the heart of T-G grammar but which also underlies nearly all of its problems. Such complaints have fueled the paradigm shift to cognitive grammar. (James D. Williams, The Teachers Grammar Book. Lawrence Erlbaum, 1999) In the years since transformational grammar was formulated, it has gone through a number of changes. In the most recent version, Chomsky (1995) has eliminated many of the transformational rules in previous versions of the grammar and replaced them with broader rules, such as a rule that moves one constituent from one location to another. It was just this kind of rule on which the trace studies were based. Although newer versions of the theory differ in several respects from the original, at a deeper level they share the idea that syntactic structure is at the heart of our linguistic knowledge. However, this view has been controversial within linguistics. (David W. Carroll, Psychology of Language, 5th ed. Thomson Wadsworth, 2008)