Licence: Public Domain Mark
Credit: Researches in embryology. (Second series) / by Martin Barry. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![294. The vesicles composing the layer {am.) on the inner surface of the mem- brane / (Plate VI. fig-s. Ill to 117., Plate VIII. fig-. 129) have each their nucleus j and nucleolus. Hence the amnion—formed as it is out of these vesicles—may be added to the structures already found to be referable to a celT'-formation. 295. The lamina in which I suppose the blood and blood-vessels to form, presented in its mode of orig-in a series of changes which do not seem to have been before ob- served in any animal, and it will be seen that they are most intimately connected with the present subject. (See par. 196. 197. 201 to 204. 211.). 296. The yelk-globules are true vesicles, containing other vesicles (Plate V. fig. 87-)- The villi of the chorion are vesicles in which I observed objects having the appear- ance of vesicles (Plate VIII. fig. 141.). The whole embryo indeed is composed of vesicles (Plate VIII. figs. 121 A. 121B. 122. and ife^.); even the primordial germ itself (Plate VI. fig. 113. bh.) seems to have been the nucleus of the vesicle in the centre of which it lies-|~. 297. I have now to mention a fact or two regarding the nature and properties of nuclei. Schleiden supposes the nucleolus to exist before the nucleus, and Schwann believes that he has observed the formation of the nucleus to take place around the nucleolus. Hence the last-mentioned observer considers that it may be said, the formation of the cell [vesicle] is only a repetition around the nucleus, of the same process through which the nucleus was formed around the nucleolusthe difference being only in degree. In connexion with this view Schwann refers to the fact, that nuclei often become hollow vesicles. On the period of origin of the nucleolus I have no observations, except that its existence was not appreciable in any of the nuclei re- presented in Plate VII. figs. 120 and 121%., and not in all of those in Plate VIII. fig. 150:|:. Several observations, however, enable me to state that objects occupying the situation of nuclei are sometimes hollow vesicles. Such for instance was their condition in the amnion (Plate VIII. figs. 129.130:|:.) and in the lamina subsequently vascular (fig. 150;}:.). I have also observed that with incipient decomposition of the peculiar granules (vesicles) of the ovisac, their nuclei appear like vesicles, filled with a colourless and pellucid fluid (Plate V. fig. 102. g.). Whether this results from distention of the nucleolus (frequently seen to be hollow), or from liquefaction of the contents of the nucleus including the nucleolus, I do not know. 299. The following observation (before noticed) may serve to extend our knowledge as to the properties of a nucleus. If Plate V. fig. 89. h. be referred to, it will be seen that the germinal spot (as such) has disappeared, and that in its stead are several vesicles with intermediate granules §. From those vesicles the germinal vesicle (c.) did not appear to differ except in its greater size. This was the eff'ect of incipient decomposition. Here then the germinal spot (possibly, as supposed by Schwann, a t See the first part of the Note to par. 186. i See the Note to par. 293. § In the ovum Plate V. fig. 86. the same phenomenon was observed, though with less distinctness.](https://iiif.wellcomecollection.org/image/b2197214x_0060.jp2/full/800%2C/0/default.jpg)
