578 New Publications. 



The next paper we may notice is that of Dr. Barry, 

 a continuation of his researches on Embryology. Being 

 aware that observations alone do not suffice in researches of 

 this nature, unless extended to the very earliest stages, he 

 again directed his attention particularly to the ovum while 

 it still remained within the ovary, and he has found that the 

 germinal vesicle is the essential portion of the ovum. This 

 vesicle becomes filled with cells after fecundation, and these 

 multiply till the vesicle becomes opaque. Dr. Barry details 

 the various stages by which this change takes place. 



It was shewn, he remarks, 

 " that in the production of the embryo out of a nucleus, layer after layer 

 of cells come into view in the interior, while layers previously formed 

 are pushed further out, each of the layers being so distinctly circum- 

 scribed as to appear 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 corresponding to that giving 

 origin to similar appearances in every nucleus 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 regard the round white spot, or cicatricula, on the yolk of the bird's 

 egg, as an altered state of the discus vitellinus in the unfecundated 

 ovarian ovum. So far from thinking that such is the case, the author 

 believes the whole substance of the cicatricula in the laid egg to have 

 its origin within the germinal vesicle, in the same manner as in the 

 ovum of mammalia. 



" The author shews that neither the germinal vesicle, nor the pel- 

 lucid object in the epithelium, is a cytoblast. He suggests, that the 

 cells into which, according to his observations, the nucleus becomes 

 resolved, may enter into the formation of secondary deposits, for 

 instance, spiral fibres, and that they may contribute to the thickening 

 which takes place, in some instances, in the cell membrane. 



