The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . at of Muscle band,phosphorescence. Subneural gland. , Posterior cellular mass. pig, Pigment spot on ganglion. Gemmiparous stolon. Lp, Process of test. to the ascidiozooids by means of a heart and system of vessels whichhave been meanwhile formed. When the cyathozooid atrophiesand is absorbed, its original atrial aperture remains and deepensto become the central cavity of the young colony, which now consistsof four ascidiozooids placed in a ring, around where the cyathozooidwas, and env
The encyclopædia britannica; a dictionary of arts, sciences, literature and general information . at of Muscle band,phosphorescence. Subneural gland. , Posterior cellular mass. pig, Pigment spot on ganglion. Gemmiparous stolon. Lp, Process of test. to the ascidiozooids by means of a heart and system of vessels whichhave been meanwhile formed. When the cyathozooid atrophiesand is absorbed, its original atrial aperture remains and deepensto become the central cavity of the young colony, which now consistsof four ascidiozooids placed in a ring, around where the cyathozooidwas, and enveloped in a common test. The colony graduallyincreases by the formation of buds from these four original ascidio-zooids. PhylocenyThe accompanying diagram Cfig. 34) shows graphically the probableorigin and course of evolution of the various groups of Tunicata,and therefore exhibits their rclafions to one another „. .q„-^much more correctly than any system of linear ^ ^ ^classification can do. The ancestral Proto-Tunicata are hereregarded as an offshoot from the Proto-Chordata—the common. ancestors of the Tunicata (Urochorda), Amphtoxus (Cephalochorda)and the Vertebrata. The ancestral Tunicata were probably free-swimming forms, not very unlike the existing are represented in the life-history of nearly all sections of theTunicata by the tailed larval stage. The Larvacea are the firstoffshoot from the ancestral forms which gave rise to the two linesof descendants, the Proto-Thaliacea and the Proto-Thaliacea then split into the ancestors of the existingCyclomyaria and Hemimyaria. The Proto-Ascidiacea gave uptheir pelagic mode of life and became fixed. This ancestral processis repeated at the present day when the free-swimming Iar\a ofthe simple and compound Ascidians becomes attached. The Proto-Ascidiacea, after the change, are probably most nearly representedby the existing genus Clavdina. They have given rise directlyor indirectly
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectencyclo, bookyear1910
