Studies from the Morphological Laboratory in the University of Cambridge, Volum 2C. J. Clay and son, 1886 |
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Vanlige uttrykk og setninger
Actinozoa adult Amphioxus appearance archenteric archenteron axial Balanoglossus Balfour becomes Beneden blastema blastodermic vesicle blastopore body cavity chick chitinous cilia close cœlom columnar connection derived described differentiation dorsal drawn in fig ectoderm elongated embryo embryonic area epiblast epiblast and hypoblast epithelium excretory flattened formation formed front end ganglion girdle gives rise glomerulus granules head kidney hind end homologous hypoblast inner mass invagination larva larvæ lateral mesoblast longitudinal section lumen median medullary groove membrane meso mesoblast mesoderm middle line mouth and anus nephridia nerve nervous system neural canal neurenteric canal notochord nucleus observations opening origin outer layer cells ovum pair Peripatus pores portion posterior pouches præoral primitive groove primitive streak protoplasm protovertebræ pubis region represented rudiment secondary cavity seen shown in fig side stage stomodæum structure suprarenal thickening tissue transverse section tube tubules uterus Vertebrata Vertebrate vide fig vitelline wall Wolffian duct yolk zona
Populære avsnitt
Side 84 - Its anterior part may have given rise to supra-oesophageal ganglia and organs of vision ; these being developed on the assumption of a bilaterally symmetrical form, and the consequent necessity arising for the sense organs to be situated at the anterior end of the body. If this view is correct, the question presents itself as to how far the posterior part of the nervous system of the Bilateralia can be regarded as derived from the primitive radiate ring. A...
Side 92 - ... forms of Vertebrata to the ingrowth of the mesoblast from the lips of the blastopore. It is, therefore, highly probable that the paired ingrowths of the mesoblast from the lips of the blastopore may have been in the first instance derived from a pair of archenteric diverticula. This process of formation of the mesoblast is, as may be seen by reference to the summary...
Side 84 - Bilateralia can be regarded as derived from the primitive radiate ring. A circumoral nerve-ring, if longitudinally extended, might give rise to a pair of nerve-cords united in front and behind — exactly such a nervous system, in fact, as is present in many Nemertines1 (the Enopla and Pelagonemertes), in Peripatus*, and in primitive molluscan types (Chiton, Fissurella, etc.).
Side 177 - The substance which from its position in the mammalian suprarenal is known as " medullary " is now almost universally admitted to consist of metamorphosed nerve-cells, which arise from one or more of the ganglia of the sympathetic system. As to the origin of the remainder, however, the so-called " cortical " substance, little is certainly known. In Elasmobranchs, Balfour1 describes the homologue of this substance as " making its appearance . . . as a rod-like aggregate of mesoblast cells, rather...
Side 81 - Coelenterate-like animal with a pouched gut, the pouching having arisen as a result of the necessity for an increase in the extent of the vegetative surfaces in a rapidly enlarging animal (for circulation and nutrition).
Side 95 - Coelenterata differ from segmented animals only in the fact that the alimentary or archenteric pouches (mesoblastic somites) and the alimentary canal do not become separate; and connected with this absence of a distinct...
Side 84 - B), this is the position this commissure ought, undoubtedly, to occupy if derived from part of a nerve-ring which originally followed more or less closely the ciliated edge of the body of the supposed radiate ancestor.
Side 128 - Kidney of Bdellostoma with a suggestion as to the origin of the Suprarenal Bodies.
Side 86 - Mollusca is that it should become the mouth. It would seem to follow from these facts, as Lankester has already pointed out, that if the blastopore is in each case homologous, then the anterior end and mouth of Serpula must be homologous with the posterior end and anus of other closely allied Chaetopods. This is manifestly absurd. There are two ways out of the difficulty ; either the homology of the blastopore must be given up, or we must suppose that primitively it gave rise to both mouth and anus,...
Side 100 - Moseley has suggested that the tracheae are homologous with the cutaneous glands of Bipalium, Hirudo, etc., while Sedgwick ('84) advances the hypothesis that "the tracheae were at first simple pits of ectoderm in a diploblastic animal, and they gradually became more complicated and branched, as the other organs also became more complicated and folded.