140 Dr Barry's Researches in Eiahryology. 



the spinal cord. These parts at first appearing granulous are 

 subsequently found to consist of vesicles. 



Thus the central portion o ithe nervous system is not ori- 

 ginally a fluid contained within a tube, but developes itself in 

 a solid form before any other part. The central portion of 

 the nervous system sometimes attains a considerable degree 

 of development, although it be exceedingly minute ; thus an 

 instance has been met with in which the development of this 

 part had reached a stage scarcely inferior to that in another 

 instance, in which the corresponding part measured more than 

 ten times the length. 



There does not occur in the mammiferous ovum any such 

 phenomenon as the " splitting" of a membrane into the so- 

 called " serous, vascular, and mucous laminae." Rathke had 

 already found that parts previously supposed by Baer and 

 others to be formed by the so-called " germinal membrane," 

 really originate independently of it ; these parts are the ribs, 

 pelvic bones, and the muscles of the thorax and abdomen, 

 which, according to Rathke, arise in a part proceeding out of the 

 " primitive trace" itself Reichert had previously discovered 

 that the part originating the lower jaw and hyoid bone 

 " grows out of the primitive trace." The author, beginning 

 with an earlier period, goes farther than these observei's, and 

 shews that the so-called " primitive trace" itself does not arise 

 in the substance of a membrane, but presents a comparatively 

 advanced stage of the object above described as the true germ. 

 Hence the author suggests there is no structure entitled to be 

 denominated the " germinal membrane." 



The most important of the foregoing facts respecting the 

 development of the mammiferous ovum, however opposed 

 they may be to received opinions, are in accordance with, and 

 may even explain, many observations which have been made 

 on the development of other animals as recorded in the de- 

 lineations of preceding obsei'vers. If in t4ie ovum of the bird 

 the germinal vesicle in like manner returns to the centre of 

 the yelk, the canal and cavity known to exist in the yelk of 

 that ovum might be thus explained. The ovum may pass 

 through at least one-and-twenty stages of development, and 

 contain, besides the embryo, four membranes, one which has 



