In Ancylomia japonica ZELLER, the process from thoracic segmentation to shortening of the embryo is divided into eight stages, and the morphogenesis in each stage is described in the present paper. 1)The premandibular appendages appear as a pair of small ectodermal processes. They exist, however, for a while and disappear in later development. 2)The head is thought to consist of six parts, i.e., the acron, the antennal, the premandibular, the mandibular, the maxillary and the labial segments. 3)At first the abdomen consists of 11 segments, but later becomes ten segments through the loss of the tenth segment. 4)At the occurring of the stomodaeal invagination the endodermal cells are formed as the special cell-mass at the blind end of the stomodaeum. On the other hand, at the occurring of proctodaeal invagination there is no special cell-mass. The anterior mid-gut epithelium originates from the cells formed at the blind end of the stomodaeum. 5)The epipharynx is formed as a small process just in front of the opening of the stomodaeum. 6)Neuroblasts are formed in each segment. Later the ganglia of the gnathal segments fuse into one. When the tenth abdominal segment disappears, the ninth and the tenth abdominal ganglia fuse into one. 7)The labrum at first appears as a pair of processes, later these paired processes move medially to fuse togather. During this process a pair of coelomic sacs in the labral anlagen is observed, but these cavities are different from those of other coelomic sacs. 8)The suboesophageal body originates from the mesodermal cells of the ventral side of the stomodaeal invagination. This mesoderm belongs to the premandibular segment. 9)The stomatogastric system develops from the dorsal wall of the stomodaeal invagination. 10)The malpighian tubules are formed as a pair of the ectodermal invaginations at the blind end of the proctodaeum. 11)The ectodermal invagination in cephalic region consists of seven pairs, i.e., the anterior tentorium, the extensor mandibulae, the flexor mandibulae, the salivary gland, the posterior tentorium, the silk gland and the prothoracic gland. The author would like to think that the anterior tentorium, the extensor mandibulae, the flexor mandibulae and the salivary gland originate from the mandibular segment, the posterior tentorium from the maxillary segment, and the silk gland and the prothoracic gland belong to the labial segment.
View full abstract