Life Histories of Animals, Including Man: Or, Outlines of Comparative Embryology

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H. Holt, 1876 - 243 páginas
 

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Página 174 - ... sea water, in which the embryo revolves. At a little later period the embryo throws off an embryonal skin, the thin pellicle floating about in the egg. Still later in the life of the embryo the claws are developed, an additional rudimentary gill appears, and the abdomen grows broader and larger, with the segments more distinct...
Página 120 - Anatomy," with the addition of the Brachiopoda, which he still retains among the Mollusca. The Onychophora, represented by Peripatus, are also omitted, as since the publication of Gegenbaur's work, Peripatus has been proved by the researches of Mr. Moseley to be a tracheate insect, for in the young genuine tracheae exist, though they disappear in the adult, or at least have not been discovered.
Página 15 - Leidy describes2 a form which he thinks "is probably a member of the genus Pelomyxa," and which is characterized by the comparatively enormous quantity of quartzose sand which it swallows with its food. "The animal might be viewed as a bag of sand !" It is from one-eighth to three-eighths of a line in diameter, and was found on the muddy bottom of ponds in Pennsylvania and New Jersey. It is possibly Pamphagus mutabilis, figured by Professor Bailey in the "American Journal of Science and Arts,
Página 35 - When fully expanded they appear round, as at cv; but when contracted they appear, observes Clark, as "fine radiating streaks, and as the main portion lessens they gradually broaden and swell unt.il the former is emptied and nearly invisible, and they are extended over half the length of the body. In this condition they might be compared to the arterial vessels of the more elevated classes of animals, but they would at the same time represent the veins, since they serve at the next moment to return...
Página 227 - The heart originates also in the head-fold at about the time the protovertebrse are formed, and the rudiment is situated below the fore gut or rudiment of the alimentary canal ; by the end of the first half of the second day it is flask-shaped, with a slight bend to the right. " Soon after its formation the heart begins to beat, its at first slow and rare pulsations beginning at the venous and passing on to the arterial end.
Página 1 - The motions of these Moners are effected by contraction of the homogeneous substance of the body, and by the irregular protrusion of portions of the body, forming either simple processes (pseudopodia) or a net-work of gelatinous threads. The food is taken in after the manner of the Amoeba, the diatom, desmid or some protozoan being surrounded by the pseudopodia and gradually enfolded by the extremely extensible body mass.
Página 133 - The worm now greatly elongates, more segments are added and it appears as in Figs. 174 and 175, with the ciliated crown, the small short tentacles and eyes. The worm now swims about slowly and creeps over the bottom, and is nearly a quarter of an inch long. It will be observed that the larva differs from those of other Annelides, as Mr. Agassiz states, in the absence of " feet, bristles or appendages of any sort, except the two tentacles of the head ; and, were it not for these, it would seem as...
Página 216 - The chL'f distinction between the fully developed branchial circulation in the Batrachian larva and that of the fish consists in the presence of small anastomosing channels, between the branchial artery and' vein of each gill, proximad of the gill itself. The tongue makes its appearance when the fore limbs are developed.
Página 238 - ... hours and was normally delivered. She had not had any fall, injury, shock or fright of serious character, and neither had the child up to the development of an attack of illness which produced the present condition. At eight years of age he had a severe attack of typhoid fever, which lasted six weeks. At the end of the third or beginning of the fourth week he became unconscious suddenly and developed paralysis, involving the entire left side. He could not move either arm or leg, but after his...

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