ATTTHORS' ABSTRACT OF THIS PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, MARCH 28 



THE DEVELOPMENT OF THE EYELIDS OF THE 

 ALBINO RAT, UNTIL THE COMPLETION OF 



DISJUNCTION 



WILLIAM H. F. ADDISON and HAROLD W. HOW 



Anatomical Laboratory, University of Pennsylvania, and The Wistar Institute of 



Anatomy 



THREE TEXT FIGURES AND TWO PLATES (THIRTEEN FIGURES) 



WTien the eyes are first formed no lids have yet appeared. 

 Then, following the formation of the lids, there is a definite 

 period when they are fused together by their epithelial margins. 

 This period varies with the different mammalian species, but is 

 more or less constant for the individuals of any one species. In 

 all, the time of formation and fusion occurs during fetal life, 

 while the subsequent separation or disjunction of the lids occurs, 

 in some species, during a later stage of fetal development, and in 

 others it does not occur until after birth. The time of disjunc- 

 tion is related, in general, to the state of development of the en- 

 tire organism, and in particular to the development of the retina. 



In the form we have studied, the albino rat, the gestation 

 period averages twenty-two days, and it is during the eighteenth 

 fetal day that the eyelids fuse. After birth the lids remain 

 closed usually for fourteen to fifteen days, and sometimes for 

 one to two days longer. In our stiidy, we have followed the 

 histological changes involved in the fusion and disjunction of 

 the lids, and have attempted to correlate the time period of this 

 process with the development of related organs. 



MATERIAL AND METHODS 



For the histological study sections were prepared of the eye 

 regions of fetuses from the seventeenth to the twenty-first days 

 of gestation, and of young animals from birth to fifteen days, at 



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