Bombyx mori breeding. Silkworm breeding is aimed at the overall improvement of silkworm from a commercial point of view. The major objectives are improving fecundity (the egg-laying capacity of a breed), the health of larvae, quantity of cocoon and silk production, and disease resistance. Healthy larvae lead to a healthy cocoon crop. Health is dependent on factors such as better pupation rate, fewer dead larvae in the mountage, shorter larval duration (shorter larval duration lessens the chance of infection) and bluish-tinged fifth-instar larvae (which are healthier than the reddish-brown ones). Quantity of cocoon and silk produced are directly related to the pupation
Crustacean larva post-larva is characterised by the use of abdominal appendages (pleopods) for propulsion. The post-larva is usually similar to the adult form, and so many names have been erected for the stage in different groups. William Elford Leach erected the genus "Megalopa" in 1813 for a post-larval crab; a shrimp post-larva is called a "parva"; hermit crab post-larva are called "glaucothoe". In the Branchiopoda, the most basal group of crustaceans, there is no metamorphosis; instead, the animal grows through a series of moults, with each moult adding various numbers of segments to the body, but without any dramatic changes in form.