The mesoderm arises for the most part from the endoderm.
The mesoderm seems to be formed entirely from the proliferation of the cells of the mesoblastic somites.
The pericycle, medullary rays, endocycle and mesoderm all form parts of one tissue system, the external conjunctive, and are only topographically separable.
- From the mesoderm most of the organs of the body - muscular, circulatory, reproductive - take their origin.
- Morphology of an Insect: the embryo of Gryllotalpa, somewhat diagrammatic. The longitudinal segmented band along the middle line represents the early segmentation of the nervous system and the subsequent median field of each sternite; the lateral transverse unshaded bands are the lateral fields of each segment; the shaded areas indicate the more internally placed mesoderm layer.