The embryology of Lytta viridana Le Conte (Coleoptera:Meloidae). V. The blastoderm, germ layers, and body segments

Abstract

This study deals with the formation of the blastoderm, germ layers, and body segments in Lytta viridana. It comprises the period of development from 16 h to 65 h. In the blastoderm the germ rudiment appears ventrally and the serosa dorsally. Two clusters of cells in the germ rudiment become visibly differentiated from the neighboring blastoderm cells. They are considered to be the endoderm. They assume later the function of secondary vitellocytes and become the centers around which are formed the yolk polyhedra. They do not give rise to the enteron rudiments. The latter arise as ectodermal outgrowths from the blind ends or the stomodaeum and proctodaeum. What is generally called gastrulation results in the inward movement of presumptive mesoderm. The view is expressed that the germ layer theory is applicable in Lytta. During development pronounced morphogenetic movements affect the blastema, the blastoderm, the germ rudiment, and segmentation. The mesoderm becomes segmented before the ectoderm. The following somites are found: labral, antennal, intercalary, 3 gnathal, 3 thoracic, and 11 abdominal. All but the last somite have coelomic sacs. The labral mesoderm is preoral from the beginning. The suboesophageal body arises as an ectodermal invagination between the intercalary and the mandibular segments. Three invaginations in the roof of the stomodaeum form the anlagen of the stomatogastric nervous system.