26 INSECT TRANSFORMATION 



nerve-cords may again be traced forwards, passing one on either 

 side of the gullet and joining the very large brain (supra- 

 oesophageal ganglion Fig. 13 br) with several pairs of distinguish- 

 able rounded lobes, innervating the eyes and feelers, and repre- 

 senting the ganglia of the foremost two or three limb-bearing 

 segments joined to those of the primitive head-lobes that are 

 formed in front of the mouth in early embryonic development. 

 All the limbs, including the feelers possibly even the eyes 

 also are, in the early embryo, behind the mouth, which 

 moves backwards as development proceeds until it comes 

 to lie between the jaws, the mandibles and maxillae. 



The nervous system of insects and their allies is particularly 

 interesting to the student of animal-structure because it is so 

 clearly built up on the same segmental plan that is conspicuous 

 in the outer body-form, and because the fusion of successively 

 situated nerve-centres may be traced not only in the develop- 

 ment of many an individual insect but also as one compares 

 related insects with one another. 



A brief reference to the reproductive system may serve to 

 conclude this survey of general insect-structure. In the abdo- 

 men of the female grasshopper are situated paired ovaries, 

 each ovary (Fig. 14 o) consisting of a set of ovarian tubes in 

 which the eggs of the insect undergo their process of growth 

 and ripening. The elongate eggs subcylindrical in shape 

 with rounded ends arranged in series along each ovarian 

 tube, give to the tube a beaded appearance, the early eggs 

 towards the narrow ends of the tubes at the dorsal region of 

 the abdomen, are minute ; as each tube is traced backwards 

 and downwards towards its opening it increases in diameter, 

 the contained eggs becoming successively larger (A) until the 

 ripened ones are ready for extrusion where the mouths of the 

 ovarian tubes on either side unite to form an oviduct (Fig. 

 14 od). The two oviducts open in the mid-ventral line into 

 a median chitin-lined passage, the vagina (Fig. 14 v), which can 

 be seen externally just in front of the eighth abdominal 

 sternum ; the eggs passing out are seized between the pro- 

 cesses of the ovipositor mentioned above. Behind the eighth 

 sternum is seen the opening of a little chitin-lined pouch the 

 spermatheca (Fig. 14 s), which receives the bundles of sperm- 

 cells from the male in the act of pairing, stores them for a 



