Organization and Morphology of the Hydromedusae.
The morphology of the group thus falls naturally into four sections - (I) the hydropolyp, (2) the polyp-colony, (3) the hydromedusa, (4) the medusa-colonies.
Since, however, medusa-colonies occur only in one group, the Siphonophora, and divergent views are held with regard to the morphological interpretation of the members of a siphonophore, only the first three of the above sub-divisions of hydromedusa morphology will be dealt with here in a general way, and the morphology of the Siphonophora will be considered under the heading of the group itself.
Hence it is convenient to consider the morphology of the medusa from these two aspects.
Brooks, Journal of Morphology, x., by permission of Ginn & Co.
The theory that the medusa is an independent individual, fully equivalent to the polyp in this respect, is now universally accepted as being supported by all the facts of comparative morphology and development.
The general theories of Siphonophoran morphology are discussed below, but in enumerating the various types of appendages it is convenient to discuss their morphological interpretation, at the same time.
That branch of biology which is termed morphology is a commentary upon, and expansion of, the proposition that widely different animals or plants, and widely different parts of animals or plants, are constructed upon the same plan.
The subjects included are systematic botany, vegetable morphology and physiology, chemistry, physics, materia medica, pharmacy, dispensing, posology, the reading of prescriptions, and a knowledge of poisons and their antidotes.
By Moor; Darwin and Acton, Practical Physiology of Plants; Davenport, C.B., Experimental Morphology, vols.
Xxxviii.; Meyer, Untersuchungen fiber die Starke-Kdrner (J ena, 1895); Montgomery, Comparative Cytological Studies, with especial regard to the Morphology of the Nucleolus, Journ.
Of Morphology, vol.
The term morphology, which was introduced into science by Goethe (1817), designates, in the first place, the study of the form and composition of the body and of the parts of which the body may consist; secondly, the relations of the parts of the same body; thirdly, the comparison of the bodies or parts of the bodies of plants of different kinds; fourthly, the study of the development of the body and of its parts (ontogeny); fifthly, the investigation of the historical origin and descent of the body and its parts (phylogeny); and, lastly, the consideration of the relation of the parts of the body to their various functions, a study that is known as organography.
It is this last department of morphology that was the first to be pursued.
Pure Morphology.Thus it became apparent that the mans and various organs of plants are, for the most part, different forms of a small number of members of the body, which have been distinguished as follows, without any reference to function.
To this it may be replied that pure morphology and organography are not alternatives, but are two complementary and equally necessary modes of considering the composition of the plant-body.
The introduction of the phylogenetic factor has very much increased the difficulty of determining homologies; for the data necessary for tracing phylogeny can only be obtained by the study of a series of allied, presumably ancestral, forms. One of the chief difficulties met with in this line of research, which is one of the more striking developments of modern morphology, is that of distinguishing between organs which are reduced, and those which are really primitive.
Di,fferentiation.Any account of the general morphology of living organisms is incomplete if it does not include some attempt at an explanation of its causation; though such an attempt cannot be carried far at the present time.
With the transition from water to land came the progressive development of the sporophyte which is the characteristic feature of the morphology of the Bryophyta and of all plants above them in the scale of life (see Bower, Origin of a Land-Flora).
LITERATURE.AS the scope of this article limits it to the general principles of the morphology of plants, comparatively few facts have been adduced.
P. Pycraft, " On the Morphology and Phylogeny of the Palaeognathae (Ratitae and Crypturi) and Neognathae," Trans.
Amongst his published works are Knowledge and Reality (q85); Logic, or the Morphology of Knowledge (1888); Essentials of Logic (1895); Psychology of.
The morphology of the abdomen, ovipositor and genital armature is dealt with by K.
The development of Aplysia from the egg presents many points of interest from the point of view of comparative embryology, but in relation to the morphology of the Opisthobranchia it is sufficient to point to the occurrence of a trochosphere and a veliger stage (fig.
A The ganglia of the nervous _ Tre system offer some important evidence as to the morphology of the head, and are alluded to below.
- Morphology of an Insect: the embryo of Gryllotalpa, somewhat diagrammatic. The longitudinal segmented band along the middle line represents the early segmentation of the nervous system and the subsequent median field of each sternite; the lateral transverse unshaded bands are the lateral fields of each segment; the shaded areas indicate the more internally placed mesoderm layer.
The Apterygogenea of Brauer and others, though we prefer the shorter term Apterygota) - is rendered improbable from the fact that existing Apterygota are related to Exopterygota, not to Endopterygota, and by the knowledge that has been gained as to the morphology and development of wings, which suggest that - if we may so phrase it - were an apterygotous insect gradually to develop wings, it would be on the exopterygotous system.
Lowne, The Anatomy, Physiology, Morphology and Development of the Blow fly (2 vols., London, 1890-1895); G.
For the morphology and classification of snails, see Gastropoda.
Same leg (see for some sug epc, The articulated movable gestions on the morphology outgrowth of the coxa, called of this leg, Pocock in Quart.
Morphology becomes a farce when such assumptions are made.
Watase, " On the Morphology of the Compound Eyes of Arthropods," Studies from the Biolog.
This division of the Vertebrata into hot and cold blooded is a curiously retrograde step, only intelligible when we reflect that the excellent entomologist had no real comprehension of vertebrate morphology; but he makes some atonement for the blunder by steadily upholding the class distinctness of the Amphibia.
A subdivision of zoology which was at one time in favour is simply into morphology and physiology, the study of form and structure on the one hand, and the study of Scope the activities and functions of the forms and structures of zoo- on the other.
No such distinction of mental activities as that involved in the division of the study of animal life into morphology and physiology has ever really existed: the investigator of animal forms has never entirely ignored the functions of the forms studied by him, and the experimental inquirer into the functions and properties of animal tissues and organs has always taken very careful account of the forms of those tissues and organs.
Cuvier's morphological doctikne received its fullest development in the principle of the " correlation of parts," which he applied to palaeontological investigation, namely, that every animal is a definite whole, and that no part can be varied without entailing correlated and law-abiding variations in other parts, so that from a fragment it should be possible, had we a full knowledge of the laws of animal structure or morphology, to reconstruct the whole.
And, though the conceptions of " archetypal morphology," to which it had reference, are now abandoned in favour of a genetic morphology.
Darwinian morphology has further rendered necessary the introduction of the terms " homoplasy " and " homoplastic " (E.
Details of the morphology of plants will be found in the articles relating to the chief groups of plants, those of animals in the corresponding articles on groups of animals, while the classification of animals adopted in this work will be found in the article ZOOLOGY.
A recent standard work on the morphology of the Hemiptera by R.
204) terms political "collectivites secondaires"; that the attributes summed up in sovereignty may be separated and divided in many ways; that there may be new forms of combinations between states or parts of states; and that their morphology is subject to no hard and fast rules.
One of the early supporters of this natural method was Augustin Pyramus de Candolle (1778-1841), who in 1813 published his Theorie elementaire de la botanique, in which he showed that the affinities of plants are to be sought by the comparative study of the form and development of organs (morphology), not of their functions (physiology).
The study of form and development has advanced under the name "morphology," with the progress of which are associated the names of K.
Structural, having reference to the form and structure of the various parts, including (a) Morphology, the study of the general form of the organs and their development - this will be treated in a series of articles dealing with the great subdivisions of plants (see Angiosperms, Gymnosperms, Pteridophyta, Bryophyta, Algae, Lichens, Fungi and Bacteriology) and the more important organs (see Stem, Leaf, RooT, Flower, Fruit); (b) Anatomy, the study of internal structure, including minute anatomy or histology (see Plants: Anatomy).
The morphology of the Hydrozoa reduces itself, therefore, to a consideration of the morphology of the polyp, of the medusa and of the colony.
Oesophagus, stomach, radial canals, ring-canal and tentacle-canals, constitute together the gastrovascular system and are lined throughout by endoderm, which forms also a flat sheet of cells connecting the radial canals and ring canal together like a web; this is the so-called endoderm-lamella (e.l.), a most important feature of medusan morphology, the nature of which will be apparent when the development is described.
As remarked in the section on morphology, the Trypanosomes as a whole are preferably regarded as including tion.
The most interesting point about the morphology is the fact that two chromatic bodies, of very unequal size, are almost invariably to be recognized.
Duckworth (Morphology and Anthro- FIG.
In England, Owen's anatomy of the pearly nautilus,14 Huxley's discussion of the general morphology of the Mollusca,17 and Lankester's embryological investigations, 19 have aided in advancing our knowledge of the group. Two remarkable works of a systematic character dealing with the Mollusca deserve mention here - the Manual of the Mollusca, by Dr S.