142 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



ganglia lying on the sides of the alimentary canal, all these 

 ganglia being connected by fine nerve-cords. 



Musculature. Lying next to the skin of the caterpillar's 

 body can be seen many muscles, some of them extending 

 longitudinally and others as transverse or circular bands. Also 

 in the head and thorax are many other muscles for moving the 

 mouth-parts and legs. Most insect muscles are small and 

 short, so that for the complete musculation of the body a great 

 many separate muscles are required. Several thousand have 

 been counted in the body of a single insect. 



The muscles which lie against the inside of the body-wall in 

 the caterpillar are repeated almost ^identically for each seg- 

 ment. This musculation then can be said to be segmental in 

 character just as we have found that the respiratory system, 

 nervous system and even the dorsal vessel can be said to be 

 segmentally arranged. That is, the internal systems of organs 

 of the insect show as plainly, almost, as the external surface of 

 the body, the fundamental segmental make-up. And they 

 also show, just as the outside of the body does, the bilateral 

 symmetry of the body. If the insect's body be cut longi- 

 tudinally by a vertical plane it will be divided into equal halves, 

 both external and internal organs either being in pairs, one 

 member on each side of this vertical plane, or being made of 

 fused pairs lying in this vertical plane. 



Reproductive System. As the caterpillar is only an im- 

 mature moth or butterfly its reproductive system is not fully 

 developed. Any adult insect of good size and not too hard wall 

 may be used to study the organs of reproduction. A grass- 

 hopper will do very well. 



In the female the eggs are produced in many small tubules, 

 called ovarioles, which are grouped to form two ovaries (right 

 and left) from each of which runs an oviduct. The two oviducts 

 unite to form a single wider short tube called the vagina. 

 From this the eggs pass out of the body in little packets. The 

 eggs are fertilized while still in the body of the female by 

 spermatozoa that have been received from the male and held 

 in a small sac called the spermatheca. Each egg is inclosed in 

 an inner, thin mtelline membrane and an outer thicker firmer 



