(1) Trichogramma evanescens lays its eggs on the egg mass of a beetle, Donacia simplex, a single parasite emerging from one host's egg.
(2) The ovum has a large germ cell determinant at its posterior pole, and in segmentation the determinant is divided among the large cells at the posterior pole, which are the germ cells.
(3) In the single case found there were two polar bodies.
(4) The blastula is fairly normal except for the curious arrangement of the chromatin in the somatic nuclei.
(5) Many nucleoli are cast out into the centre of the egg, where they collect till from twenty-five to fifty are present; the mass is then extruded on the periphery of the egg.
(6) As the blastoderm grows it broadens without lengthening up to the stage where the germ layers begin to form.
(7) About thirty-five nuclei sink inwards from the dorsal surface of the embryo to form endoderm.
(8) From the blastoderm stage to that of the gastrula no nuclear division appears to take place.
(9) Shortly after the formation of the endoderm amitosis may be found, and from this onwards the number of nuclei increases.
(10) The mesoderm seems to be formed from peripheral nuclei, which sink in sporadically; no somites can be made out, nor does any segmental method of formation of the mesoderm occur.
(11) The nervous system, stomodæum, and probably proctodæum, are normally formed.
(12) The germ cells lie in a pocket formed be several somatic cells, which embrace them.
(13) Ordinary mouth parts, tracheæ, heart, and œsophageal valve are wanting; the head has two horn-like mandibular processes, which may assist in scooping forwards the food.
(14) The larva does not feed on the food little by little, defecating as it eats; instead, it begins by swallowing all the yolk at once, so that its body becomes enormously distended and stretched.
(15) Metameric external segmentation is absent, the body and head being continuous and sac-like.