ENTOMOLOGY

COCKROACHES 875When numerous they congregate, especially in kitchens where it is warm,damp, and not overly clean. On shipboard they often abound to such anextent as to cause much damage, in some cases entire supplies of certainfoods being spoiled by eating, or rendered nauseous by their contact, adisagreeable odor being imparted by secretions from certain scent-glands,situated in the bodies of the insects. The readiness with which they arctransported with food supplies make their introduction into militaryand other camps a matter of great probability, and when once infested,such places are soon thoroughly stocked with these skulking creatures ..BIOLOGYThe life histories of our household roaches are very similar. The eggs.are deposited incased in an oblonl;f, leathery pod, called an ootheca, andcontaining several eggs each, arranged in two longitudinal rows. In some·cases this ootheca is carried around for some time by the I]lother roach"partially protruding from the tip of the abdomen. But generally they aredeposited in some cranny and sometimes the ootheca of Periplaneta isglued in folds of clothing, or in a leaf if of outdoor occurrence, andcovered over with bits of matcrial chewcd off by the insect. I have myself'seen instances of this, once on a garment and twice on leaves, and therecognition of the ootheca in such cases is not at all clear until it is.uncovered._When first hatched from the egg the young roach resembles the adultin general form, but is apterous and the body is soft and whitish in color.Soon, however, the chitin becomes oxidized and the normal color appears.A number of molts occur during growth, the old skin splitting along thedorsal line of the thorax, and through this slit the insect emerges, theprocess being one, requiring some considerable exertion; every part ofthe body sheds its old covering, antennae, feet and all. The freshly moltedroach, like one newly hatched, is whitish in color, but a few hours serveto restore the natural colors. In the last two instars the wings appear ina rudimentary condition, at the last molt appearing fully developed.This appearance of rudimentary wings is the only character separatingthe stages of -the roach which correspond to larva and pupa of insectswith complete metamorphoses. The terms larva and pupa are not generallyapplied to insects with incomplete metamorphoses, the term nymphbeing there used, the degree of development being indicated by the numberofthe instar, or period between two molts. A single roach may produceseveral egg-masses in a season, and in the common house species the periodof development from egg to adult varies with the food supply, climaticconditions, etc.'Vhile in some tropical and subtropical regions certain species of