At a later stage of development of the Graafian vesicle, 

 its fluid content corresponds to the compact part of the 

 protein in the chicken egg. Then polar differences in the 

 fluid appear: on one side it is more transparent, and on the 

 other there appears an aggregation of granular material. 

 Thus, the cumulus is formed with the embryonic disk, and 

 the ovule situated there becomes increasingly separated by 

 the forming membrane. Next, the central area appears in 

 the ovule since its granules become attached to the periphery. 

 In this, according to Baer, the general principle of development 

 in the centrifugal direction becomes apparent. 



On the question about the origin of the corpus luteum, 

 Baer disputed the current opinion that this was a new 

 formation, unrelated to the Graafian vesicle. Instead, he 

 tried to establish an indication that the corpus luteum 

 resulted from growth of the internal layer of the theca in 

 the empty Graafian vesicle. This completely corresponds with 

 modern ideas, but now it is known that the hypertrophy of 

 the corpus luteum walls takes place at the expense of the 

 follicular epithelium, and not at the expense of the internal 

 theca as Baer thought. The elements of the internal theca 

 are only preserved in the radial connective tissue partitions, 

 which correspond to the folds of the rupturing vesicle. 



The ovule separated or released from the Graffian vesicle 

 falls into the funnel in the fallopian tube and then into the 

 uterus, where it is covered with fibers. The development of 

 the embryo in the mammalian ovum, according to Baer, "was in 

 the same manner as in birds." First of all, he claimed, the 

 spina dorsalis appears. H From it grow the spinal plates 

 (laminae dorsalis) , which correspond to the primary or 

 primitive folds (plicae primitivae) of Pander, and soon the 

 ventral or abdominal plates (laminae ventrales) . All 

 vertebrates undergo one type of development, namely growing 

 centrifugally; hence the two plates are directed upwards and 

 form a plane for the spinal and head brain, and two plates 

 are directed downwards. A plane for the internal parts and 

 vascular stems forms there. 



11. By this term Baer designated that formation to which, 

 in UBER ENTWICKLUNGSGESCHICHTE, he gave the name 

 accepted in modern embryology, primary region. 



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