Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . Ova of Sepia officinalis. * CCCXCI. 636 LECTURE XXIV. line membrane near the narrower end of the egg ; and, when thefolds of the vitelline membrane have been obliterated in the detachedegg, the germ-vesicle has disappeared or become obscured throughthe effect of impregnation. The influence of the resulting impregnatedvesicle, or primary germ-cell, extends over only a small part of theyolk, like the cicatricula of the birds egg. The fission of thatgerm-cell manifests its
Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . Ova of Sepia officinalis. * CCCXCI. 636 LECTURE XXIV. line membrane near the narrower end of the egg ; and, when thefolds of the vitelline membrane have been obliterated in the detachedegg, the germ-vesicle has disappeared or become obscured throughthe effect of impregnation. The influence of the resulting impregnatedvesicle, or primary germ-cell, extends over only a small part of theyolk, like the cicatricula of the birds egg. The fission of thatgerm-cell manifests itself by two slightly elevated prominences, as atJig. 232, A, a, in each of which is a secondary nucleated cell. The next 232. stage shows four prominences (ib. b) ; these by their fission formeight {ib. c), of a triangular form, becoming more acute, and theapex of each showing the hyaline nucleus: and now spontaneous fis-sion manifests itself in another direction, and the apices of each seg-ment seem to be detached, each fission-sphere (ib. d, a) having, likeeach fission-segment (5), its proper nucleus. This figure showsthe sixteenfold division, affecting the central cells (a) as well as thesegments (5). The progressive multiplication of sperm-force-centresmultiplies the peripheral segments, and fills the central space withsmaller and more numerous derivative germ-spherules. The germ-mass thus formed may be divided into two layers, andthe outer surface becomes smooth. Its further increase by fission-growth and confluence of germ-cells manifests itself by slight eleva-tions from this cambium {^g. 233) ; the first of these is a medianrhomboid one, which is the basis of the 233 trunk or mantle-sac (a); two smal
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Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1850
