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XV. Researches in Embryology. First Series. By Martin Barry, M.D. F.R.S.E., 

 Fellow of the Royal College of Physicians in Edinburgh. Communicated by 

 P. M. RoGET, M.D. Sec. R.S. 



ReceivedJune 20, — Read June 21, 1838. 



IT has been truly said, that " in all the sciences of observation, the great diffi- 

 culty generally consists in taking the first steps." A hundred and fifty years have 

 now elapsed since the celebrated Regner de Graaf, after a series of well-conducted 

 observations, maintained that the ovum of the Mammalia must exist already formed in 

 the ovary ; an opinion which, after meeting with violent opposition, appears to have 

 been nearly abandoned, and superseded by the notion countenanced by Haller, that 

 the ovum was formed in the Fallopian tube out of a substance discharged from the 

 ovary. A century after De Graaf had promulgated his opinions, Cruikshank 

 arrived at the same conclusion, that the ovum was really formed in the ovary ; but he 

 sought it there in vain. Prevost and Dumas in 1824 obtained a glimpse of something 

 that must have been the ovum in that organ ; Von Baer in 1827 found and recognised 

 it there. 



This important discovery of Baer formed an epoch in the history of development ; 

 but it was a " first step," and the object one of extreme minuteness. It was there- 

 fore not surprising if the excellent discoverer did not see or justly estimate all that 

 appertained thereto ; and he said himself " there remains yet many a thing that will 

 become a prize "^ for others. 



Von Baer for instance did not see the germinal vesicle contained within the mam- 

 miferous ovum ; he saw no more than a transparent space. This, however, was an 

 oversight of the first importance, because that which gives peculiar interest to the 

 germinal vesicle is the fact, now generally acknowledged, that it is the most essential 

 portion of the ovum ; and besides, as in the following pages I shall have to show, this 

 structure and its contents are the earliest that appear in the order of formation. 

 Overlooking the germinal vesicle in the Mammalia, Von Baer supposed the ovum 

 itself to represent, in that class of animals, the germinal vesicle of Birds-f-. Other 

 analogies, and they are not few, which he based on this were consequently erroneous. 



I have thought it proper to make these introductory remarks, because of the neces- 



t Professor Baer called the vesicle he discovered in the ovary, not the ovum but the " ovulum." If, how- 

 ever, it can be made to appear extremely probable that the chorion or external membrane of the ovum of the 

 uterus is a primitive part of the ovarian vesicle of Baee, it is perhaps better to call the latter an ovum, as will 

 be done in this memoir. 



