DEVELOPMENT OF EYELIDS OF ALBINO RAT 



25 



Schweiger-Seidl's observations on the process of separation 

 in human fetuses were long quoted, and the figure illustrating 

 the fused lid margins, which was pubhshed in 1866, is still m 

 use in text-books of embryology. He regarded as the chief 

 agencies in the separation, 1) the keratinization within the hair 

 folhcles developing from the conjoined epithelium and, 2) the 

 formation of spaces between the cells of the junction epithelium 

 by the secretion from the sebaceous and tarsal glands. 



Contino ('07) studied a larger series of human fetuses, and 

 considered that the separation of the corners of the hd margins 

 was due to the secretion from the sebaceous and tarsal glands 

 and that the separation of the intermarginal epithelium was due 

 to the cornification of the central layers of cells. 



Ask ('08), in addition to human fetuses, examined also a series 

 of kittens, of which, however, he gives no description or figures, 

 but says he found the conditions in both practically the same. 

 He places the cornification process in the junction epithelium 

 as the most important factor in separation. Cornification also 

 proceeds from the hair folhcles into the junction epithelium, and, 

 thirdly, there is an independent cornifying process in the pos- 

 terior part of the junction epithelium. 



In our study of a consecutive series of rats of known ages, 

 both fetal and postnatal, we have made measurements of the 

 junction epithelium, and thereby have been able to attempt an 

 analysis of the growth stages of the junction epithehum, and we 

 have also correlated the period of fusion of the hds with certain 

 stages of development of the skin and hair and with the his- 

 togenesis of the retina. 



SUMMARY 



The time of formation and fusion of the eyehds in the albino 

 rat is a definite one, occurring during the eighteenth day of 

 fetal hfe; hence observation of the presence or absence of the 

 fused hds in a fetal rat will determine whether the fetus is older 

 or younger than eighteen days. 



The formation of the hds in this animal is a relatively rapid 

 process; at the seventeenth day of fetal hfe there are only slight 



