DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGY. 303 



timately united with the substance of the ovary, so that in general it is not so very 

 easy to dissect the vesicle freely out on all sides without laceration -f-." 



Plate VII. fig. 62;}: presents the parts which Baer considers to enter into the forma- 

 tion of a Graafian vesicle. For an explanation of this figure I refer to the description 

 of the plate. It appears to me however, as I shall endeavour presently to show, that 

 a " Graafian vesicle" is an ovisac that has acquired a covering proper to itself, and as 

 such the term will be used in the present paper. 



The figure just referred to, exhibits the situation of the " ovulum" (ovum) of Mam- 

 malia, according to Baer, surrounded by its so-called " disc" within the Graafian 

 vesicle. It will be shown in this memoir that there is no structure in. the Graafian 

 vesicle of a discoid form ; and the error of Baer in mistaking the " ovulum" (ovum) 

 of Mammalia for a part corresponding to the germinal vesicle of other animals, ap- 

 pears to be attributable in part to his misconception of the situation of the "ovulum" 

 (ovum) in reference to its surrounding granules. 



PuRKiNJE § questioned the analogy which Baer had imagined between his " ovu- 

 lum" (ovum) of the Mammalia and the germinal vesicle of other animals ; and the 

 discovery at length by Coste in France, and by Valentin and Bernhardt in Ger- 

 many, of a germinal vesicle in Mammals, showed the justness of Purkinje's reason- 

 ing, increasing the analogy between the bodies expelled respectively from the ovaries 

 of Mammalia and those of other vertebrated animals. It will presently be shown 

 that a perfect analogy does not exist between these bodies. 



One of the last additions made to our knowledge in embryology, exceeding in mi- 

 nuteness all the rest, is the discovery by Professor Rudolph Wagner ||, on the in- 

 ternal surface of the germinal vesicle, of the macula germinativa, or germinal (germi- 

 native) spot. 



The object of this memoir is to add some discoveries of my own on the early stages 

 of the ovum, not only of the Mammalia, but of the other Vertebrata. This cannot 

 be done except by means of details both minute and, I fear, fatiguing ; but perhaps 

 I may venture to hope for the reader's indulgence when he recollects the precision 

 requisite in treating a question comparatively new in the history of physiology. The 

 perusal would, however, be much facilitated by occasional reference to the following 

 tabular Synopsis of the parts to be described. It might also be advantageous to ex- 

 amine the plates (V. to VIII.) in connexion with this table ; for as the same letters 

 denote the same objects in all the figures, and as these letters have been introduced 



t Translation from the German, in the Edinburgh Medical and Surgical Journal, No. 127 ; which contains 

 the early part of Professor Valentin's elaborate work " Handbuch der Entwickelungsgeschichte des Menschen 

 mit vergleichender Riicksicht der Entwickelung der Saugethiere und Vogel," Berlin, 1835. 



X Taken from Baer, Lettre sur la Formation de I'CEuf, translated by Breschet, Paris, 1829. fig. ix. (I have 

 not the original at hand.) 



§ Encyclopadisches Worterbuch, Band x. Artikel "Ei," pp. 124 — 128, Berlin, 1834. 



II Lehrbuch der Vergleichenden Anatomic, S, 351, Leipzig, 1834-5. Edinburgh Medical and Surgical 

 Journal, No. 127. Prodromus Historiae Generationis Hominis atque Animalium, Lipsise, 1836. 



