Amphioxus sentence example

amphioxus
  • In accordance with this view there would be also some probability in favour of regarding the collar nerve-tube of the Enteropneusta as the equivalent of the cerebral vesicle only of Amphioxus and the Ascidian tadpole, and also of the primary forebrain of vertebrates.
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  • The branchial bars which constitute the borders of the clefts are of two kinds: - (i) Septal bars between two contiguous clefts, corresponding to the primary bars in Amphioxus; (2) Tongue bars.
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  • From serving primitively as the essential organ of the cleft the tongue-bar may have undergone reduction and modification, becoming a secondary bar in Amphioxus, subordinate to the primary bars in size, vascularity and development; finally, in the craniate vertebrates it would then have completed its involution, the suggestion having been made that the tongue-bars are represented by the thymusprimordia.
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  • The respiratory current of water is therefore conducted to the exterior by different means from that adopted by Amphioxus, and this difference is so great that the theory which seeks to explain it has to postulate radical changes of structure, function and topography.
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  • The vascular system does not readily lend itself to morphological comparison between such widely different animals as Balanoglossus and Amphioxus, and the reader is therefore referred to the memoirs cited at the end of this article for further details.
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  • In the direct development Bateson showed that the three divisions of the coelom arise as pouches constricted off from the archenteron or primitive gut, thus resembling the development of the mesoblastic somites of Amphioxus.
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  • Kolliker (Development of Cephalopods, 1844), Remak (Development of the Frog, 1850), and others had laid the foundations of this knowledge in isolated examples; but it was Kovalevsky, by his accounts of the development of Ascidians and of Amphioxus (1866), who really made zoologists see that a strict and complete cellular embryology of animals was as necessary and feasible a factor in the comprehension of their relationships as at the beginning of the century the coarse anatomy had been shown to be by Cuvier.
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  • The theoretical interest of Amphioxus depends upon a variety of circumstances.
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  • Although it is true that there is a certain amount of gradation in the degree of development to which these organs have attained in the various orders, yet it is hardly sufficient to enable the imagination to bridge over the gap which separates Amphioxus from the lowest fishes in regard to this feature of organization.
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  • The ordinal name for the genera and species of Amphioxus is Cephalochorda, the term referring to the extension of the primary backbone or notochord to the anterior extremity of the body; the family name is Branchiostomidae.
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  • With regard to its habits, all that need be said here is that while Amphioxus is an expert swimmer when occasion requires, yet it spends most of its time burrowing in the sand, in which, when at rest, it lies buried with head protruding and mouth wide agape.
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  • Amphioxus favours a littoral habitat, and rarely if ever descends below the 50-fathom line.
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  • Amphioxus is a small fish-like creature attaining a maximum length of about 3 in., semitransparent in appearance, showing iridescent play of colour.
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  • Alimentary, Respiratory and Excretory Systems. - Although the function of the two latter systems of organs is the purification of the blood, they are not usually considered together, and it is therefore the more remarkable that their close association in Amphioxus renders it necessary to treat them in common.
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  • - Amphioxus lanceolatus laid open ventrally.
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  • These may be called the spinal eyes, and it is said that they are disposed in such a way as to receive illumination preferentially from the right side, although this fact has no relation with the side upon which Amphioxus may lie upon the sand.
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  • The development of Amphioxus possesses many features of interest, and cannot fail to retain its importance as an introduction to the study of embryology.
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  • One point must not be omitted, namely, the homogeny of the endostyle of Amphioxus and the thyroid gland of Craniata.
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  • Boveri, "Die Nierencanalchen des Amphioxus," Zool Jahrb.
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  • Schneider, "Einiges fiber Resorption and Excretion bei Amphioxus lanceolatus," Anat.
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  • He compares the tube heart of an embryo to that of the primitive chordate, Amphioxus.
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  • 8), seen in solid tentacles as a row of cubical vacuolated cells, occupying the axis of the tentacle, greatly resembling notochordal tissue, particularly that of Amphioxus at a certain stage of development; as a fourth variety of endodermal cells excretory cells should perhaps be reckoned, as seen in the pores in the foot of Hydra and elsewhere (cf.
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  • Sub-phylum c. Cephalochorda (see AMPHIoxus).
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  • - In ?/?/ i / the Acrania (Amphioxus) the ???
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  • On account of the absence of anything in the nature of a skull, Amphioxus has been regarded as the type of a division, Acrania, in contrast with the Craniata which comprise all the higher Chordata.
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  • It is important to emphasize the fact that in Amphioxus the excretory tubules are co-extensive with the gill-clefts.
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  • - Diagram of embryo of Amphioxus seen from above in optical section.
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  • In 1883-1886 Bateson showed by his embryological researches that the Enteropneusta exhibit chordate (vertebrate) affinities in respect of the coelomic, skeletal and nervous systems as well as in regard to the respiratory system, and, further, that the gill-slits are formed upon a plan similar to that of the gillslits of Amphioxus, being subdivided by tongue-bars which depend from the dorsal borders of the slits.
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