Observations on Budding in Paludicella and Some Other Bryozoa

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Museum, 1891 - Bryozoa - 114 pages
 

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Page 50 - ... generation II. are more numerous than those derived from the middle two. Finally, it is evident that the number of individuals per unit of arc will be the same for arcs of all radii, and therefore the rate of increase of individuals will diminish through successive generations. In Crisia eburnea, Linn.,1 we find the same laws illustrated. The architecture of the genus has been carefully treated of by Smitt ('65% pp. 115-142) as forming the basis of classification. Barrois ('77, pp. 76-85) has...
Page 107 - Gymnolpemata (pages 31, 63, 103). The atrial opening first arises at a late period by separation of the cells of the neck. The communication plate arises in Paludicella as a circular fold of the layers of the body wall, the mesodermal cells at the centre of which become cnticularized.
Page 106 - Gymnolsemata probably (pages 8, 11, 12, 69). The inner layer of the body wall is also embryonic in the budding region, as indicated by the fact that ova arise near the neck of the polypide, in PhylactolEemata at least (page G8).
Page 100 - The inner laver of the polypide bud is composed of cells derived from the rim of the blastopore, and they are to be regarded as still indifferent, and as first becoming differentiated into ectoderm and entoderm in the formation of the young polypide.
Page 106 - The outer layer of the body wall in the budding region is one of rapidly assimilating and rapidly dividing tissue ; the inner layer of the body wall becomes...
Page 51 - ... lateral edges. As in other species, they become very firmly attached to stones and other objects, and form creeping stolons, from which (as well as from rootlets which are not attached in this way) fresh stems may originate. The colonies do not so often consist of a single main stem as in C. eburnea. It is frequently remarked that the longest and most branched parts of the colony are lateral branches, and not parts of the main stems.
Page 23 - ... in the continuity of the lophophore is more prominent. By the completion of the union of the lophophores in front of the anus, the rectum is quite cut off from communication with the intertacular space. It now opens only into the thin-walled, funnel-shaped depression of the atrial cavity. Pari...
Page 36 - ... few are filled with vacuoles and their highly refractive bodies. The conditions of the mesodermal cells at the tip are slightly different from those found elsewhere. Usually, instead of many small vacuoles, one finds only one or two which fill almost the entire cell, — sometimes perfectly homogeneous in structure, sometimes containing small highly refractive granules. These appearances I believe to be explicable only upon the assumption that the...
Page 79 - Nahrthier to a joint. This could doubtless be determined, however, by studying the early stages in the development of the stocks. Taking them as they are, however, we find a very simple condition in the stocks of Class I., in which the Nahrthiere are arranged in a single row, as in Vesicularia spinosa (cf.
Page 26 - Phylactolsemata, arises as an outgrowth of the brain. Serial sections show that the ganglion suddenly diminishes in size immediately below the point at which the circumoral nerves arise, but one can trace a layer of cells continuous with the brain downwards for ten or fifteen micra farther, to near the cardiac valve. At this point one can still see nuclei of a third layer lying between the digestive epithelium of the valve and the mesoderm.