Ectothermy

“ If the beginnings or absorbent mouths of the venous system remain torpid, petechiæ or vibices are produced in fevers, similar to those which are seen in scurvy without fever. If the skin was frequently moistened for an hour, and at the same time exposed to the common air, or to oxygen gas, it might contribute to turn the black colour of these points of extravasated blood into scarlet, and thus by increasing its stimulus facilitate its reabsorption? For oxygen gas penetrates moist animal membranes though not dry ones, as in the lungs during respiration. ”

“ The extremities of the vessels become charged with unctuous matter; the deadened cellules of the epidermis are covered with a varnish, which is partly insoluble in water, and this internal accumulation and external coating prevent the skin from performing its functions, which are not confined to those of shielding the body, but are essential to the chemical processes within. The skin has analogous duties to those of the lungs, supplying oxygen to the blood at the extremity of its course, and when most completely in need of it. ”

“ The walls of the air-vesicles, and coats of the blood-vessels, are similar, in their mechanical arrangement, to the membranous bladder in the before described experiment. As the oxygen of the air has greater affinity for blood than for nitrogen, so it permeates the membranes that intervene between the air and blood more readily than the nitrogen. As the carbonic acid and water have a greater affinity for air than for the other elements of the blood, so they will also pass through the walls of the blood-vessels and air-cells more readily than the other elements of the dark-colored blood. ”

“ OF THE OXYGENATION OF THE BLOOD IN THE LUNGS, AND IN THE PLACENTA.
I. Blood absorbs oxygene from the air, whence phosphoric acid changes its colour, gives out heat, and some phlogistic material, and acquires an ethereal spirit, which is dissipated in fibrous motion. II. The placenta is a pulmonary organ like the gills of fish. Oxygenation of the blood from air, from water, by lungs, by gills, by the placenta; necessity of this oxygenation to quadrupeds, to fish, to the fœtus in utero. Placental vessels inserted into the arteries of the mother. Use of cotyledons in cows. ”

“ The distinction first established separates the office of transforming other energy into mechanical motion, from the office of liberating the energy to be so transformed. While in the layer between endoderm and ectoderm are arising the rudiments of the muscular system, there is marked out in the ectoderm the rudiment of the nervous system. ”

“ It is not necessary to describe in detail the beginnings of all the various structures which arise from that important layer of cells in the embryo which is termed the ectoderm; but since it gives rise to that part of the embryo, which eminently places man in the first place in the world of animals, we may select it for a little further description. We may leave out of account the beginnings of the skin and the glands, and some other parts, and look for the moment at the origin of the nervous system, which includes the brain, the spinal cord, and the whole nervous mechanism of the individual. ”

“ Figure 11a passes through the tip of the head. Dorsal to the embryo is the ectoderm and a thick mass of yolk (y) . The amnion (a) is seen as an irregular membrane which entirely surrounds the head. The medullary canal (mc) is entirely closed except at the extreme anterior end, which is bent downward so that the opening is on the ventral side. The nervous (nl) and epidermal (ep) layers of the ectoderm are in contact throughout, but are clearly distinguishable because of the difference in the compactness of their cells. ”

“ The general secernent organ of the whole body together with all its systems is the sexual system, which having been elevated by virtue of this general character to the rank even of an animal, is a true sexual animal. That which is a general and not a partial excretion, is imparted by the sexual animal. It is the animal reversed.
2936. Thus the secernent organ of the general circulation must belong to the sexual system, and perform in it that which the liver, or in other words the reverse of the lungs, has done in the splanchnic circulation. The kidneys are the lungs reversed. ”

“ The function of the seminal fluids, therefore, appears to be to restore to the aging tissues this property, this animal matter, which when in its right ratio and proportion in the cells of the organism produces the condition of youth. The action of these seminal fluids, therefore, seems to be two-fold, a dissolving and a nourishing. The distinction should be clearly made that the action is NOT merely stimulating. The stimulation of a nerve-cell is a temporary excitement. ”

“ In all the sections of this stage the ectoderm and entoderm are fairly thick in the region of the embryo proper, but become thinner until reduced to a mere membrane as we pass to more distal regions. Both layers are composed of loosely arranged cells, with scattered nuclei. Where the ectoderm becomes thickened to form the medullary folds, the cells are much more compactly arranged ”

“ The heart, in some of the Loliginidæ, lies within the genital chamber, but is not enclosed in a special receptacle. The membrane, forming the wall of the chamber, is apparently reflected over it, though it is so completely incorporated with the surface of the organ as not to be demonstrable. In the Octopodidæ the heart lies in the cellular tissue, between the renal and genital chambers, and is more or less enveloped by the wall of the former : but here, as in the other group, there is no pericardial sac.
The heart itself is strong and muscular, and the fibres are of the striated kind. ”

“ He then discusses the relationship of the parts in the embryo, and arrives at the conclusion that “in embryos, whilst the lungs are in a state of inaction, performing no function, subject to no movement any more than [203] if they had not been present, Nature uses the two ventricles of the heart as if they formed but one for the transmission of the blood.” He therefore concludes that the condition of the embryos of those animals which have lungs, whilst these organs are yet in abeyance or not employed, is the same as that of the animals which have no lungs. ”

“ For instance, in the case of the third nerve of Scyllium the differentiation appears to take place earliest near the ciliary ganglion, and to proceed from that point to the base of the mid-brain.
There are two main methods in which new organs are developed. In the one, which indicates the possibility of physiological continuity, the organ arises by the direct modification of a portion of a pre-existing organ; the development of the central nervous system of the Vertebrata Coelom. from a groove in the embryonic ectoderm may be taken as an example of this method. ”

“ The ectoderm rarely consists of more than one layer of cells: these are divisible by structure and function into nervous, muscular and secretory cells, supported by interstitial cells. The endoderm is generally also an epithelium one cell in thickness, the cells being digestive, secretory and sometimes muscular. Reproductive sexual cells may be found in either of these two layers, according to the class and sub-class in question. ”

“ It is sufficiently manifest that this general function becomes more clearly marked-off from the others, at the same time that it becomes itself parted into subordinate functions.
In a developing embryo, the functions or more strictly the structures which are to perform them, arise in the same general order. A like primary distinction very early appears between the endoderm and the ectoderm—the part which has the office of accumulating energy, and the part out of which grow those organs that are the great expenders of energy. ”

“ The otocysts and eyes are formed as invaginations of ectoderm, the former behind the eyes, at the sides of the funnel. All the nerve-centres, cerebral, visceral, pedal and optic, are formed as proliferations of the ectoderm. At the sides of the optic ganglia a pair of ectodermic invaginations are formed, which in the adult become the white bodies of the eyes, surrounding the optic ganglion. These are vestiges of lateral cerebral lobes which degenerate in the course of development. ”

“ There is no skull, and the notochord is not surrounded by any vertebral column. There are no limbs nor paired fins. There is no exoskeleton, and the ectoderm is a single layer of non-ciliated columnar cells. The mouth is ventral and anterior, the anus is ventral, posterior, and asymmetrically placed on the left side. The pharynx is a large branchial sac, having its sides perforated by many gill-slits, and is surrounded by an ectodermal enclosure, the atrium, which opens to the exterior by a median ventral atriopore. ”

“ Between these two there presently arises the mesoderm in which becomes visible the rudiment of that vascular system, which has to fulfil the intermediate duty of transferring energy. Of these three general functions, that of accumulating energy is carried on from the outset: the endoderm, even while yet incompletely differentiated from the ectoderm, absorbs nutritive matters from the subjacent yelk. The transfer of energy is also to some extent effected by the rudimentary vascular system, as soon as its central cavity and attached vessels are sketched out. ”

“ In the kidney, the substances secreted by the cells, being of no farther use, are at once ejected from the body. Hence the renal tissue may be spoken of as excretory. In the epithelium cells of the lungs, the protoplasm plays an altogether subordinate part in the assumption of oxygen and the excretion of carbonic acid. ”

“ A continuous layer of cells, therefore, is everywhere to {141} be found on both the external and the internal free surfaces of the body. So far as these cells belong to the proper external wall of the body, they constitute the ectoderm, and so far as they belong to its proper internal wall, they compose the endoderm. Between these two layers of nucleated cells lie all the other parts of the body, composed of connective tissue, muscles, vessels, and nerves ”

“ Dal took a deep breath and began running the anatomical atlas tapes through the reader, checking the critical points of Moruan anatomy. Oxygen-transfer system, circulatory system, renal filtration system—at first glance, there was little resemblance to any of the "typical" oxygen-breathing mammals Dal had studied in medical school. ”

“ The plates forming the corona are, like all the elements of the skeleton of Echinodermata, products of the connective tissue which underlies the ectoderm, which in Echinoidea remains in a fully developed condition covering the plates, and does not, as in Ophiuroidea, dry up so as to form a mere cuticle. The ectoderm consists of the same elements as that of Asteroidea, viz. delicate tapering sense-cells with short sense-hairs, somewhat stouter supporting cells and glandular cells. ”

“ Figure 6g is nearly one third the length of the embryo posterior to the preceding and passes through the posterior third of the embryo. The medullary thickening of the ectoderm (ec) is marked, but shows no sign of a medullary groove; in fact, the median line is the most elevated region of the ectoderm. The notochord (nt) is larger in cross-section than in the more anterior regions. It is still continuous with the entoderm (en) and is fairly closely attached to, though apparently not continuous with, the mesoderm (mes) on each side. ”

“ The reproductive 98 organs or gonads are borne on the mesenteries, the germinal cells being derived from the inner layer or endoderm.
In common with all Coelenterate animals, the walls of the columnar body and also the tentacles and peristome of Actinia are composed of three layers of tissue. The external layer, or ectoderm, is made up of cells, and contains also muscular and nervous elements. The preponderating elements of the ectodermic layer are elongated columnar cells, each containing a nucleus, and bearing cilia at their free extremities. ”

“ With the growth of the ectosome we necessarily get a corresponding development of the proximal portion of the inhalant canal-system. At first the ectosome is merely a thin membrane, the dermal membrane, pierced by the inhalant pores, which are usually arranged in groups. Beneath the groups of pores (pore-areas) lie spacious subdermal cavities which form the commencement of the inhalant canal-system in the choanosome. In more advanced types the ectosome becomes greatly thickened and may be specially strengthened in a variety of ways to form a cortex. ”

“ There can be no doubt whatever that the whole of the skeleton of these animals is formed by the ectoderm, and is external to their bodies. If we could get rid of the influence of tradition upon our use of popular expressions we should call this skeleton a shell. There can be little doubt, moreover, that this skeleton is formed by a single layer of specialised ectoderm cells called the "calicoblasts." ”

“ The motive power is supposed to have its source in the contractility of the ectoplasm. The endoplasm is held to be a passive stream, not an active stream as Ewart supposed to be the case in plant cells. The power of contractility is held to be due to the process of gelation of endoplasm into ectoplasm, which is due to a change of phase, the fluid part of the endoplasm becoming dispersed and thereby developing surface energy in proportion as the amount{86} of surface of the fluid is increased. This increase of surface produces the phenomenon of contractility. ”