Anal pit --> proctodeum
1. An ectodermally lined depression under the root of the tail, adjacent to the terminal part of the embryonic hindgut; at its bottom, proctodeal ectoderm and cloacal endoderm form the cloacal plate. When this epithelial plate ruptures, the anal and urogenital external orifices are established.
Synonym: anal pit.
2. Terminal portion of the insect alimentary canal, extending from the pylorus (area of malpighian tubule attachment) to the anal opening; in certain diptera (flies) and other insects, the proctodeum is divided into a tubular anterior intestine and an enlarged posterior intestine, or rectum, ending at the anus.