348 Papers from the Department of Marine Biology. 



gus occurred in mammals and in man. Kreuter describes also similar 

 obliterated areas in the mid-gut and hind-gut of fetuses between the 

 fourth and tenth weeks. In four human embryos, measuring from 8.4 to 

 16 mm., Lewis (1912) describes an esophagus whose lumen is pervious 

 throughout; however, he describes vacuoles in the epithelial lining of 

 these stages similar to those described by Kreuter as stages in the 

 opening of the soHd esophagus. But he regards an atresia of the 

 esophagus in the human embryo as abnormal at all stages (p. 368). 



It would seem that an embryonic normal atresia of the esophagus is a 

 widespread phenomenon among vertebrates, and is essentially similar 

 from elasmobranch fishes to man. 



The phenomenon has not yet, as far as I am aware, been described for 

 turtles, a circumstance which adds to the interest of this investigation ; 

 nor have its intimate spatial relationship to the respiratory anlage and 

 its probable functional significance been hitherto pointed out. 



This work is based chiefly on embryos of the loggerhead turtle, 

 Caretta (Thalassochelys) caretta, but enough has been seen also in 

 embryos of the snapping turtle {Chelydra serpentina) and of Chrysemys 

 marginata to warrant the statement that in these forms a substantially 

 identical process occurs. 



In occasional pig embryos also, from 8 to 12 mm. length, I have 

 noticed short areas of occlusion in the esophagus. 



More or less extensive atresia occurs also in the stomach, duodenum, 

 and other portions of the small intestine, large intestine, and rectum 

 in certain of the above-named forms, especially in mammals. Of these 

 regions the duodenum is most commonly occluded. The character of 

 the occlusion and the manner of the reestablishment of patency are 

 in general here also through the agency of originally discrete inter- 

 epithelial vacuoles which gradually coalesce. In the turtle Caretta no 

 other portions of the alimentary tract were at any stage similarly 

 occluded. 



MATERIAL. 



The material consists of a series of 26 loggerhead-turtle embryos 

 ranging from the second to the thirty-second day of incubation. It was 

 collected in the summer of 1914 during a visit to the Laboratory of 

 Marine Biology of the Carnegie Institution of Washington, located 

 on Loggerhead Key, Florida. I am greatly indebted to Dr. Alfred 

 G. Mayer for the excellent facilities afforded for securing and preserving 

 a large number of specimens, approximately 200. 



Two fixing fluids were employed almost exclusively, namely, the 

 Zenker-formol modification of Helly and the strong chrom-aceto- 

 osmic solution of Flemming. After the Helly fixation, different sets 

 of sections were variously stained with the Giemsa solution, the iron- 

 hematoxylin mixtures of Heidenhain, and the Delafield's hematoxylin 

 and eosin combination. 



