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The world lay in clearest, barest, coldest light, its hopeless deceit and its misery all revealed! It was well that a grumous fog pervaded the air, each atom a spike in a vesicle of darkness! it was well that no summer noon was blazing about the world! At least there was no mockery now! the world was not pretending to be happy! was not helping the demon of laughter to jeer at the misery of men!
In this fact, and the fact we have already established that the Gastraea has been evolved from the hollow vesicle of the one-layered Blastaea, and this again from the original unicellular stem-form, we have obtained a solid basis for our study of evolution. The second section, that leads from the Gastraea to the Prochordonia, is much more difficult and obscure.
The cell then looks just like an ordinary animal ovum. When it has been in this condition for some time the cell divides into two, four, eight, sixteen, thirty-two, and sixty-four cells. These arrange themselves in a round vesicle, thrust out vibratory lashes, burst the capsule, and swim about in the same magosphaera-form with which we started.
But the plan or fundamental scheme of these eyes is correct and capable of indefinitely greater development than the organs of touch or smell, perhaps greater even than the otolith vesicle. And the reflex influence of the eye on the brain was the greatest advantage of all.
The brain from above, v fore brain, z intermediate brain, m middle brain, h hind brain, n after brain. The brain with the uppermost part of the cord, from the left. In the Cyclostoma a stage above the Acrania the fore end of the cylindrical medullary tube begins early to expand into a pear-shaped vesicle; this is the first outline of an independent brain.
One can hardly conceive the beauty of the egg as seen through the microscope at this period of its growth, when the whole yolk is divided, with the dark granules on one side, while the other side, where the transparent halo of the vesicle is seen, is brilliant with light.
We call this layer the blastoderm, and the sphere itself the blastula, or embryonic vesicle. This interesting blastula is very important. The conversion of the morula into a hollow ball proceeds on the same lines originally in the most diverse stems as, for instance, in many of the zoophytes and worms, the ascidia, many of the echinoderms and molluscs, and in the amphioxus.
Whether the whole of any species was at once translated forward, or only a few parents were employed to give birth to the new type, must remain undetermined; but, supposing that the former was the case, we must presume that the moves along the line or lines were simultaneous, so that the place vacated by one species was immediately taken by the next in succession, and so on back to the first, for the supply of which the formation of a new germinal vesicle out of inorganic matter was alone necessary.
The remains of the yelk, which have not yet been applied to the nutrition and growth of the young animal, are contained in a sac attached to the rudimentary intestine, and termed the yelk sac, or 'umbilical vesicle. Two membranous bags, intended to subserve respectively the protection and nutrition of the young creature, have been developed from the skin and from the under and hinder surface of the body; the former, the so-called 'amnion, is a sac filled with fluid, which invests the whole body of the embryo, and plays the part of a sort of water-bed for it; the other, termed the 'allantois, grows out, loaded with blood-vessels, from the ventral region, and eventually applying itself to the walls of the cavity, in which the developing organism is contained, enables these vessels to become the channel by which the stream of nutriment, required to supply the wants of the offspring, is furnished to it by the parent.
In modified small-pox each pustule is, as in unprotected small-pox, inflamed at the base; while in chicken-pox there is only very slight redness around each vesicle. The vesicles in chicken-pox are small much smaller than the pustules in modified small-pox. Is Hooping-cough an inflammatory disease?
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