DEPARTMENT OF EMBRYOLOGY.* 



Franklin P. Mall, Dieector. 



The following report deals for the most part with studies in embry- 

 ology that have been published during the past year. The subjects 

 may be grouped under three headings : cytology, human embryology in 

 general, and neurology. 



CYTOLOGY. 



The work accomplished in the last ten years in the field of cytology 

 has gone far to improve our knowledge of the structure of the proto- 

 plasm, from the fact that it has cleared the field of several theories 

 and at the same time has harmonized others which seemed to be 

 irreconcilable. In the study of the embryonic protoplasm with the 

 special technique required, one of the most important advances has 

 been made. This work — started by Meves on the embryos of birds 

 and extended to mammals, amphibians, invertebrates, and, during the 

 past winter, to fishes by Professor Jules Duesberg — has given harmoni- 

 ous results. It has been shown that the cytoplasm of the undifferen- 

 tiated cell, in addition to the centrioles and the more or less abundant 

 and non-permanent yolk granules, contains a ground-mass in which 

 bodies of various and changeable form, the chondriosomes, are 

 embedded. It is in these undifferentiated embryonic cells that investi- 

 gators have found the chondriosomes the easiest to define by utilizing 

 their chemical as well as their moiphological properties. A careful 

 study of the behavior of the chondriosomes during the evolution of the 

 cell has shown that they are able to move, apparently freely, in the 

 surrounding mass, and consequently that such things as a reticular 

 structure of the protoplasm and an alveolar structure in Biitschh's 

 sense (whose theory, by the 'wa.y, is very much open to criticism from 

 the physio-chemical point of view also), most probably do not exist. 

 The field has furthermore been cleared of the so-called ''chromidial" 

 theory — the chondriosomes belong to the protoplasm. As already 

 stated, the chondi'iosomes appear in various forms, sometimes as 

 granules, sometimes as filaments which may be branched or even 

 connected in a network, or, at other times, as one large body. This is 

 frequently the case in the spermatid of invertebrates. Again they 

 assume different shapes in the various phases of the life of a cell, as is 

 best shown in the evolution of the male germ-cells. 



On the other hand, it has been repeatedly established by various 

 observers that Benda's ''mitochondria" were not previously unknown 

 elements of the cell, but that they have already been noted in many 

 tissues and had been described under various names. For instance, 



♦Address: Johns Hopkins Medical School, Baltimore, Maryland. 



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