. A manual of elementary zoology . Zoology. MANUAL OF ELEMENTARY ZOOLOGY Reproduc- tion. separation. which leads an independent existence. It will be con- venient to use the word "fission" to denote the actual breaking away of the new body, for reproduction is more than a mere act of This will be seen if we consider it a little more closely. (a) As has been said, reproduction always involves the fission of an existing body. Life never arises anew, but is always passed on from one living being to another which arises from it. A living being which divides to produce others is a parent;
. A manual of elementary zoology . Zoology. MANUAL OF ELEMENTARY ZOOLOGY Reproduc- tion. separation. which leads an independent existence. It will be con- venient to use the word "fission" to denote the actual breaking away of the new body, for reproduction is more than a mere act of This will be seen if we consider it a little more closely. (a) As has been said, reproduction always involves the fission of an existing body. Life never arises anew, but is always passed on from one living being to another which arises from it. A living being which divides to produce others is a parent; those which it forms are offspring. (b) The offspring are always at first unlike the parent. There are, as we shall see, certain animals in which the only evident differ- ence between the off- spring and the in- dividual by whose division they arose is the necessary one of size. But in the great majority of cases there is also an obvious difference in form, the offspring being at first very unlike the parent in structure. This difference is obscured in the case of man and some other animals, where the offspring undergoes changes in the womb before birth (Fig. i), but it is seen unmistakably in animals which are born in the condition of an egg. In their immature con- dition the offspring are known as reproductive bodies. (c) In spite of this unlikeness at starting, the offspring become in time like the paretit from which they arose, owing to a succession of changes which is sometimes straightfor- ward, or direct, sometimes, as in the well-known case of the butterfly, very roundabout, or indirect. Thus the life. Fig. i.—The egg or "ovum'' from which a human being is developed, highly Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Borradaile, L. A. (Lancelot Alexander), 1872-1945. London :
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1920
