Dr Barry's Researches in Embryology. S7 



question. Thus it is very common to meet with several varie- 

 ties of epithelium-cells in the oviduct, including those which 

 carry cilia, filled with cells ; but the whole embryo at a subse- 

 quent period is composed of cells filled with the foundations of 

 other cells. 



In the second series of these researches, it was shewn that 

 the mulberry-like object above mentioned is found to contain 

 a cell larger than the rest, elliptical in form, and having in its 

 centre a thick-walled hollow sphere, which is the nucleus of 

 this cell. It was further shewn that this nucleus is the rudi- 

 mental embryo. From what has been just stated, it appears, 

 that the same process by which a nucleus in one instance 

 transforms itself into the embryo, is in operation in another 

 instance, where the product does not extend beyond the inte- 

 rior of a minute and transitory cell. Making allowance, in- 

 deed, for a difference in form and size, the description given 

 of the one might be applied to the other. It was shewn in 

 the second series, that in the production of the embrj^o out of 

 a nucleus, layer after layer of ceils come into view in the inte- 

 rior, while layers previously formed are pushed further out ; 

 each of the layers being so distinctly circumscribed as to ap- 

 pear almost membranous at its surface. The same membranous 

 appearance presents itself at the surface of the several layers 

 of a nucleus in many situations. Further, in the formation of 

 the embryo, a pellucid centre is the point around which new 

 layers of cells continually come into view ; a centre con*espond- 

 ing to that giving origin to similar appearances in every nu- 

 cleus described in the present memoir. It was shewn that in the 

 embryo this mysterious centre is present until it has assumed 

 the form of the cavity, including the sinus rhomboidalis, in the 

 central portion of the nervous system. 



The process above described, as giving origin to the new 

 being in the mammiferous ovum, is no doubt universal. The 

 author thinks there is evidence of its occurrence in the ova of 

 batrachian reptiles, some osseous fishes, and certain of the 

 mollusca ; though the explanation given of these has been of 

 a very different character. It has hitherto been usual to re- 

 gard the round white spot, or cicatricula, on the yolk of the 

 bird's laid ^^g^ as an altered state of the discus vitellinus in 



