660 



CLASS IV. INSECTA. 



five ovarian caeca which in the young are segmentally arranged as are the 

 three pair of caeca which make up the testes on each side. The family 

 is a widely distributed one, the best known British form being Lepisma 

 saccharina (Fig. 413), the " silver-fish " which is found only in or near 

 human dwellings, in old cupboards, sugar barrels, etc. The other British 

 Lepismid is Thermobia furnorum, which lives in bake-houses. 



Group II. ANAPTERYGOTA. 



Wingless insects whose ancestors probably were winged. Para- 

 sitic on Vertebrates. The first two Orders with very slight meta- 

 morphosis, the third with complete metamorphosis. 



Order 3. MALLOPHAGA.* 



Wingless with flat bodies and large heads ; prothorax distinct, the 

 meso- and meta-thorax small and the latter often fused with abdomen. 

 The insects of this order are usually termed Bird-lice, but as they 

 do not live exclusively on birds the term Biting-lice has been re- 

 cently substituted. They live amongst the feathers of birds or 

 the hairs of mammals, crawling about the bases of these epidermal 

 structures. Their bodies are flattened and their heads exhibit 

 a great variety of shape. The antennae are short with but three 



to five segments ; the eyes are reduced or 

 absent ; the mandibles toothed, the first 

 maxillae are mere lobes which are said 

 to bear no palps, the second maxillae or 

 labium have in two families well-developed 

 palps, but these are absent in another sub- 

 division. The segments of the abdomen 

 which are apparent, vary in number from 

 eight to ten. The legs have usually a 

 one- or two-segmented tarsus ; rarely 

 three segments occur ; the tarsi end in one 

 or two claws, and in the former case the 

 claw is especially fitted to the hair of the 

 animal which harbours the insect. 

 The ventral nerve cord is concentrated in the thorax there 

 being no abdominal ganglia. The ova are laid amongst the 

 hairs or feathers. The young resemble their parents very 



* Giebel and Nitzsch, Insecta Epizoica, 1874. Grosse, Zeitschr. wiss. 

 Zool., xlii, 1885, p. 530. Melnikow, Arch. Naturg. xxxv, 1869, p. 154. 



FIG. 414. Menopon pal- 

 lidum ; inhabits the com- 

 mon fowl, Gallus domesti- 

 ciis (after Piaget). 



