PHYLUM ARTHROPODA 



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-the antennae of the latter not being represented. On this view 

 the homologies of the anterior appendages in the two animals may 

 K.-> rt ~.oorwi j n the following table : 



COCKROACH. 



Antennae. 



Absent. 



Mandibles. 



First maxillae. 



Second maxillae (labium). 



First legs. 



Second legs. 



Third legs. 



CRAYFISH. 



Antennules. 

 Antennae. 



Mandibles. 

 First maxilla?. 

 Second maxillae. 

 First maxillipedes. 

 Second maxillipedes. 

 Third maxillipedes. 



; 



add.c 



Representatives of the five pairs of thoracic legs of the Crayfish 

 would thus appear to be absent in the Cockroach, and evanescent 

 rudiments, no traces of which remain in the adult, alone represent 

 in the latter the well-developed 

 abdominal appendages of the 

 former. 



In the living Cockroach re- 

 spiratory movements are to 

 be observed, in which the ab- 

 domen becomes alternately ex- 

 panded and contracted ; these 

 movements bring about the 

 alternate inhalation and ex- 

 halation of air through certain 

 apertures the stigmata at 

 the sides of the body. Two 

 of these are situated on each 

 side of the thorax, one be- 

 tween the prothorax and meso- 

 thorax, and the other between 

 the mesothorax and the meta- 

 thorax. Eight occur on each 

 side in the abdomen between 

 the terga and sterna of the 

 segments. Just internal to 

 each spiracle the main trachea 

 into which it leads presents an 

 elastic ring or spiral, acting as 

 a valve for closing the passage. 



The principal sets of muscles of the trunk of the cockroach 



are (1) the longitudinal sternal muscles (Fig. 456, long, stern.), 



which form a transversely segmented sheet, extending between 



- adjoining sterna of the thorax and abdomen ; (2) oblique sternal 



l-'ic. 4 :>i;. Ventral portion of the muscular 

 system of the Cockroach. </</. cox, ad- 

 ductor of coxa ; ab<l. cox. abductor of coxa ; 

 cxt. Jem. extensor of femur ; Ixt f, ,-. stem. 

 first tergo-stemal ; long, stern, longitudinal 

 sternal; ol>l. stern, oblique sternal. (After 

 Miall and Denny.) 





