ANATOMY OF AN ARTHROPOD. 



93 



' The ahdominal appendages are seldom found in Hexapods : 

 when present, they are never in the form of looomotory organs, 

 except in Crustacea and Myriapoda. In our type we see only 

 the anal cerci before mentioned. The anus is situated beneath 

 the tenth abdominal tergum and between the podical plates. 



Fig. 33.— Stiluctube of Insect Leg. 



a, Coxa; b, trochanter; c, feiaur ; d, tibia ; p, tibial spur ; /, metatarsus ; 

 g, tarsus ; h, ungues. 



The spiracles (fig. 35, Spi), or breathing pores, are at the sides 

 of the thorax and abdomen ; they are twenty in number. On 

 the thorax one pair will be seen between the pro- and meso- 

 thorax, another between the meso- and metathorax, and others 

 on each side of the first eight abdominal segments. They are 

 in the form of slit-like oval openings, with branched processes 

 running across them. 



Internal Anatomy of the Cockroacli, 



By dissecting the cockroach under water we can gather a fair 

 knowledge of the general anatomy of an arthropod with consider- 

 able ease. On removing the chitinous covering of the thorax 

 and abdomen very carefully, there will be exposed a straight 

 chambered tube running along the middle line of the thorax 

 and abdomen. This is the so-called insect heart. Lateral slit- 

 like openings along the sides of this organ are called the ostia, 

 through which the blood returns to the heart, to be pumped out 



