Quarterly Journal of Microscopical Science, Vol s2-78, 91-131, Copyright © 1935 by Company of Biologists

Memoirs: Observations on the Embryology of Corynodes Pusis (Coleoptera, Chrysomelidae)

¹ University of the Witwatersrand, Johannesburg

An account is given of the embryology of Corynodes pusis Marsh, a Chrysomelid beetle feeding on Asclepias fruticosa. The development of this species is remarkably similar to that of Euryope terminalis, an allied species previously investigated by the writer (1931, 1932).

In both species there is a very early differentiation of the germinal protoplasm at the posterior pole, and the genital rudiment makes its appearance in this position immediately the blastoderm is completed.

The lower layer of cells is derived by proliferation and invagination of cells in the mid-ventral line, and this process is considered to represent the gastrulation phase of other invertebrate embryos. The cells resulting from this invagination differentiate into lateral mesoderm and median endoderm. The mesoderm gives rise to appendicular and segmental muscles, fat-body, cardioblasts, and the muscle-layer of the mesenteron.

The epithelial layer of the mid-gut is considered to develop from the median endoderm, which gives no indication in either of these species of a bipolar condition. In this respect the development of these two species differs from that of other recently investigated insects, but shows some resemblance to the condition described by Leuzinger and Wiesmann (1926) in the Orthopteran, Carausius morosus.

The development of the ectoderm is essentially similar to that of other insect embryos. The stomodaeum and proctodaeum are imaginations of the ectoderm, as are also the respiratory and excretory systems. In addition to the two pairs of thoracic and eight pairs of abdominal spiracles observed in Euryope, there are vestigial spiracular invaginations on the ninth and tenth abdominal segments of Corynodes. In both species the Malpighian tubules arise as three separate pairs of outgrowths of the wall of the proctodaeum, and there is no indication that any part of their wall is derived from the endoderm, an opinion recently expressed by Henson (1932) when describing the condition in the embryo of Pieris.

The tentorium is rather better developed in Corynodes than in Euryope, and in the embryo four pairs of cephalic ectodermal invaginations were observed to arise in a series one behind the other on the antennary, mandibular, maxillary, and labial segments.