Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . and contain fewerova, than in the Loligo. The eggsof the Cuttle-fish are of comparativelylarge size, of an oval form, attenuatedat the extremities, and each envelopedin a lamellated horny covering, whichis prolonged into a short cleft pedicle at one extremity, and attachedby it to some foreign body: numbers of these ova are generally foundclustered together, and they have commonly received the name ofsea-grapes {Jig. 231). Of the many noble contributions to Embryology,
Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . and contain fewerova, than in the Loligo. The eggsof the Cuttle-fish are of comparativelylarge size, of an oval form, attenuatedat the extremities, and each envelopedin a lamellated horny covering, whichis prolonged into a short cleft pedicle at one extremity, and attachedby it to some foreign body: numbers of these ova are generally foundclustered together, and they have commonly received the name ofsea-grapes {Jig. 231). Of the many noble contributions to Embryology, which scienceowes to German physiologists, none surpass in importance that *from which the following remarks have been abridged. At the beginning of the development of the egg, in Sepia officiinalis, the germ-vesicle with its nucleus is surrounded by a smallquantity of colourless yolk, and all the parts of the egg grow, butthe germ-vesicle in a less ratio than the yolk. When the germ-vesicle has reached its full size the yolk increases and acquires itscharacteristic colour. The srerm-vesicle advances close to the vitel-. 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
Size: 1219px × 2050px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorowenrichard18041892, bookcentury1800, bookdecade1850
