Malpighian tubules arrest early in their morphogenesis in homozygous embryos. The tubules are typically spherical at stages 16 and 17 (when they are elongated in wild-type embryos) and sometimes the tubules fail to form protuberances at all in mutant embryos. The tip cells are seldom apparent and may be absent. The tubules remain fairly small, apparently ceasing cell division soon after they bud. The hindgut is usually shorter than normal and sometimes drastically so.
Very little ventral cell invagination is seen by mid to late germ band extension.
Nusslein-Volhard.
C. Nusslein-Volhard.