Researches in embryology. (First series) / by Martin Barry.

Date:
1839
Catalogue details

Licence: Public Domain Mark

Credit: Researches in embryology. (First 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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    4. Its size when first formed is exceedingly minute. I have found it in several orders of Mammalia measuring not more than the 50th of a Paris line-|~ in length. Such is the case, for instance, in the Ox (Plate V. fig. 4. h.); so that a cubic inch would contain upwards of two hundred millions, not merely of the elements of the ovum, but of the ovisacs of this animal. The minuteness of these vesicles indeed is almost incredible. In the Dog I have seen them measuring only the 100th of a Paris \\n&\ (Plate V. fig. 9. h.), thus little more than one third the long diameter of a blood-granule (red particle) of the Proteus anguimis^. 5. The ovisac is more or less pellucid according to its size; being most so in the early stages of formation, and becoming merely translucent as development advances. This is partly owing to the gradual addition of an external covering or tunic, to be hereafter more particularly mentioned (24. 25.). It continues iiowever in all its stages more translucent than the substance in which it lies. Cavity in which the Ovisac is often found. 6. More particularly considered, the situation of the ovisac in its early state is often found to be a cavity (Plate VIII. fig. 69.), sometimes, as already said, in the proper substance {stroma) of the ovary, and sometimes in the parietes of a Graafian vesicle. It lies loose in, and unconnected with the walls of, its containing cavity. That it does so is shown<.in the figure just referred to (fig. 69.), which presents an ovum, f\ escaped from the ovisac, h, and lying external to the latter in the cavity. (This change in the situation of the ovum was seen to take place on the ovisac being burst under the microscope by means of the compressor; when the ovum became squeezed into an elliptic form. This has repeatedly occurred |].) The cavity in which the ovisac lies, may sometimes be found after the latter has been pressed out of it. The proper membrane of the Ovisac in Mammalia. 7. In ovisacs of the minutest size this membrane is perfectly transparent; yet in and near to its contour it looks as though it were concentrically lamellar^ (Plate V. figs. 9. 11. 12. h.). I apprehend this appearance to arise from plaits or folds occur- ring in the membrane under pressure even at that early period, and indicating great susceptibility of distention. Its thickness is relatively very considerable in the smaller t That is, about the 562nd of an English inch. See the table of measurements (118.), for a simple mode of reducing the fraction of a French line (') into the fraction of an English inch. X = yjVj of an English inch. § Through the kindness of Professor R. Wagner I possess a living specimen of this animal, and have re- peatedly confirmed the observation first made by him, that the red particles of its blood measure in some In- stances of a Paris line in length, and that they are visible with the naked eye, being larger than those of any other animal the blood of which has been examined. II The ovum in this instance was ruptured before escaping, and left its germinal vesicle, c, behind. f The appearance liere referred to has been observed by R. Wagner, who uses the above expression in de- scribing what he considers minute Graafian vesicles (Beitrage, &c., S. 28.).