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Atresia of the Esophagus in the Embryo of the Loggerhead Turtle Caretta Caretta a Normal Developmental Condition

occluded, embryos, kreuter, day and solid

ATRESIA OF THE ESOPHAGUS IN THE EMBRYO OF THE LOGGERHEAD TURTLE (CARETTA CARETTA): A NORMAL DEVELOPMENTAL CONDITION.

In a series of embryos of the loggerhead turtle collected and used originally for a study of the history of the primordial germ-cells, it was noticed that the esophagus was solid for a greater or less extent, approximately from the point of origin of the respiratory anlage to its bifurcation into the bronchi, from the eleventh to the thirty-second day of incubation. At the latter stage the esophagus is still occluded at its oral end, though now fenestrated for a considerable extent caudally; and it seems probable that the esophageal atresia persists practically to near the end of the incubation period (8 weeks) at the level just behind the opening of the larynx.

The points of special significance in regard to this material are: (1) the relatively longer persistence of the occlusion than has yet been described for any other form; (2) the absence of contributory yolk in the stenosed area; (3) close relation to the point of origin of the respira tory anlage, which fact may disclose its possible functional significance.

Balfour was the first (1878) to describe a similar phenomenon in the esophagus of certain selachii. Kreuter (1903) confirmed these obser vations in the case of Pristiurus and Torpedo. Dean (1897) reports a solid esophagus in larvae of Anzio calva. An occluded esophagus is said to occur also in certain bony fishes—e. g., herring, trout, salmon (Balfour, Oppel). In cyclostomes the esophagus remains patent throughout development (Kreuter). In certain amphibia (Bufo, Rana) the esophagus becomes occluded, in part through the medium of contributory yolk-globules (Meuron, 1886) ; and the same is true for certain reptiles (Anvil fragilis, Oppel, 1891; Lacerta, Meuron, 1886). According to Meuron, the esophagus of the chick embryo of the fifth day is occluded for a length of 115 microns, but regains partial patency again in the sixth day through the appearance of vacuoles. Lillie de scribes the esophagus of the chick embryo as completely occluded immediately behind the glottis from the eighth to the eleventh day, "owing to proliferation of the lining cells."

Kreuter (1905) was the first to describe an epithelial obliteration of the esophageal lumen in the human embryo, contrary to the teaching of Kollmann and other embryologists that no solid stage of the esopha 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 solid 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 Corea(' no other portions of the alimentary tract were at any stage similarly occluded.