PHYLUM ARTHROPODA 



313 



ceptacle where sperm are received. The last sternites and appendages 

 are greatly modified to aid in copulation and in carrying the eggs. As 

 the eggs are laid and fertilized they are covered with secretions from a 

 pair of accessory glands. The two glands secrete dissimilar materials 

 that react in the presence of air to produce a tanned protein cover. 

 The case thus formed is carried about until the eggs hatch. Young 

 cockroaches resemble adults but lack wings; they mature in seven molts. 



I 



143. Classification of the Insecta 



Insects are divided into the wingless subclass, Apterygota, and a 

 winged subclass, Pterygota. The former includes the silverfish (order 

 Thysanura) and springtails (order Collembola) (Fig. 16.16). 



The Pterygota are divided by paleontologists into the Paleoptera, 

 in which the wings are held permanently at right angles to the body, 

 and the Neoptera, in which the wings are folded back over the body 

 when not in use. Paleopterans were abundant in ancient times, and 

 included many orders now extinct. Surviving are the dragonflies and 

 damselfiies (order Odonata) and mayflies (order Ephemerida) (Fig. 16.23), 

 groups that have aquatic young. The adults are forced to stay out in the 

 open to avoid breaking their wings, and have flight as the only means 

 of escape. Neopterans, with hinged wings, not only can escape by flight 

 but also may run fast or hide in crevices. It is interesting in this respect 

 that, although wingless species are found in all of the neopteran orders, 

 none of the living or extinct paleoptera are wingless. 



Figure 16.23. Living Paleoptera. Orders Odonata (left) and Ephemerida (right). 

 Adults above, and nymphs below. (After Borror and DeLong.) 



