Bütschli. Entwicklungsgeschichte der Biene. Ib., Bd. XX. (1870).
Bobretzky. Bildung d. Blastoderms u. d. Keimblätter bei den Insecten. Ib., Bd. XXXI. (1878).
Nusbaum. Rozwój przewodów organów pteiowych u owadów (Polish). Kosmos. (1884). [Development of Sexual Outlets in Insects.]
---- Struna i struna Leydig’a u owadów (Polish). Kosmos (1886). [Chorda and Leydig’s chorda in Insects.]
The Embryonic Development of the Cockroach. [174]
By JOSEPH NUSBAUM, Magister of Zoology, Warsaw.
The development of the Cockroach is by no means an easy study. It costs some pains to find an accessible place in which the females regularly lay their eggs, and the opaque capsule renders it hard to tell in what stage of growth the contained embryos will be found. Accordingly, though the development of the Cockroach has lately attracted some observers, the inexperienced embryologist will find it more profitable to examine the eggs of Bees, of Aphides, or of such Diptera as lay their eggs in water.
The Cockroach is developed, like most animals, from fertilised eggs.[175] The eggs of various animals differ much in size and form, but always contain a formative plasma or egg-protoplasm, a germinal vesicle (nucleus), and a germinal spot (nucleolus). Besides these essential parts, eggs also always contain a greater or less quantity of food-yolk, which serves for the supply of the developing embryo. The quantity of this yolk may be small, and its granules are then uniformly dispersed through the egg-protoplasm; or very considerable, in which case the protoplasm and yolk become more or less sharply defined. Eggs of the first kind are known as holoblastic, those of the second kind as meroblastic, names suggested by the complete or partial segmentation which these kinds of eggs respectively undergo. When the food-yolk is very abundant it does not at first (and in some cases does not at any time) exhibit the phenomena of growth, such as cell-division. If, on the other hand, the yolk is scanty and evenly dispersed through the egg-protoplasm, the segmentation proceeds regularly and completely. The eggs of Arthropoda, including those of the Cockroach, are meroblastic.
The eggs of the Cockroach (P. orientalis) are enclosed (see p. [23]) sixteen together in stout capsules of horny consistence. They are adapted to the form of the capsule, laterally compressed, convex on the outer, and concave on the inner side. The ventral surface of the embryo lies towards the inner, concave surface of the egg. Each egg is provided with a very thin brownish shell (chorion), whose surface is ornamented with small six-sided projections. In young eggs, still enclosed within the ovary, the nucleus (germinal vesicle) and nucleolus (germinal spot) can be plainly seen, but by the time they are ready for deposition within the capsule, so large a quantity of food-yolk, at first finely—afterwards coarsely—granular, accumulates within them, that the germinal vesicle and spot cease to be visible.