The Neurenteric Canal in the Frog,Rana Pipiens.

Abstract

Even the temporary appearance of a tubular connection in the embryo between the neurocoel and the hindgut, known as the neurenteric canal, has considerable phylogenetic significance if its presence can be demonstrated and the parts homologized in such a variety of forms as Amphioxus, Fish, Amphibia, Reptiles, Mammals and possibly even in birds (duck, goose, Sterna., Lillie 1 ). It is the purpose of this paper to add another link in the chain of evidence of the embryological existence of such a canal, using the Anuran, Rana pipiens.

The neurenteric canal has been variously described as a tubular connection between the neurocoel and hindgut; the post-anal gut (Shumway 2 and Huettner 3 ); the dorsal cavity of the closing blastopore; the short bent posterior portion of the neurocoel plus the remains of the blastopore; the notochordal canal; the anterior end of the primitive streak; and also the connection between the amniotic and yolk sacs of the mammal. Huxley and DeBeer, 4 for instance, are very cautious in stating that with the approximation of the parallel neural ridges at that region so that “in this manner, a neurenteric canal, actual or virtual, according as to whether the blastopore is or is not still open, is formed, connecting the cavities of the neural tube and the gut.”

Over 100 frog embryos (Rana pipiens) of stages 15 to 17 (Shumway 5 and Rugh 6 ) were serially sectioned sagittally at 10 μ and examined for the possible existence of this canal. In practically every embryo the canal was either present as such (Fig. 1) or its lining of pigmented dells could be easily discerned (Fig. 2).