302 DR. MARTIN BARRY'S RESEARCHES IN EMBRYOLOGY. 



sity that lies before me, in offering the present contribution in embryology, for pointing 

 out several other structures connected with the discovery of Baer, the nature of which 

 I believe this author to have mistaken, and some that appear to have escaped his 

 notice. This I shall do with great deference, asking his re-inspection of the parts, and 

 respectfully soliciting an examination of them by other physiologists who have been 

 engaged in researches on the early stages of the ovum of the Mammalia, especially 

 Professors Purkinje, Krause and Coste ; but more particularly Professor Valentin 

 and my valued friend Professor Rudolph Wagner. 



In the course of this investigation, which occupied many months, the number of 

 individual animals examined was very large, furnishing me an opportunity for veri- 

 fying most of the facts by repeated observation. The examinations were generally 

 made very soon after death ; and the drawings having been all taken by myself, I 

 have it in my power to say that their fidelity may be relied upon-f-. 



In the year 1837, preparatory to the commencement of my own researches, I spent 

 some time in Germany for the purpose of becoming acquainted with the known 

 facts on animal development and other objects of microscopic research ; and cannot 

 omit this opportunity of gratefully acknowledging the facilities afforded me on that 

 occasion by my honoured friends Professors Johann Muller, Ehrenberg, Rudolph 

 Wagner, and Dr. Th. Schwann. The microscope I use is an achromatic, since 

 made for me by Schiek of Berlin, and similar in all respects to the instrument em- 

 ployed by Professor Ehrenberg. 



It may not be improper in the first place to furnish an idea of what has been 

 already published on some branches of the subject ; for it is one to which the atten- 

 tion of physiologists in this country has scarcely begun to be directed. 



Valentin gives the following comprehensive description of the vesicles of Graaf: — 

 " In the ovary of each of the Mammalia, there is found a greater or less number 

 of spherical pellucid vesicles, the so-called /b///cw// Gtraqfiani^ (Graafian vesicles,) the 

 greater part of which are situated near the surface of the organ. Their size is very 

 different, as well in different animals as in the same ovary of the same animal, since 

 the older ones are sometimes four to five times, as in Rabbits, Dogs, Cats ; some- 

 times eight to ten times, as in Man ; sometimes ten to twenty times, as in rumi- 

 nating animals ; sometimes thirty to fifty times, and still more, as in the Swine ; 

 larger than those recently formed, and this, too, independently of their increase in 

 volume after impregnation. When situated close to the surface, they are covered by 

 the peritoneum alone ; when deeper, by the latter, and by the fibrous tissue of the 

 ovary, and closely invested by a net-work of vessels, between which there is a gra- 

 nular membrane. They are everywhere closed, without a trace of processes, but in- 



t Some of the figures to be seen to advantage should be viewed with a large lens. 



