ARTHUR DEWITT WHEDOX 395 



at the apex of the eighth segment. No accessor}- sacs were made 

 out. The cord-hke appearance of the ovaries indicates well 

 formed egg tul)es within them. 



At this stage the ovipositor (external) is quite complete. Its 

 three pairs of gonapophyses reach beyond the apex of the tenth 

 sternite. 



The Nerve (^ord 

 (Plate XXI, figure 1) 



The work on this system is limited to the studj?- of the ventral 

 nerve cord or chain. In general plan the Odonata are like other 

 insects in this respect. In the thorax there are three very large 

 and closely approximated ganglia. There are eight abdominal 

 ganglia, but after the earlier larval stages the first ganglion is 

 drawn forward as first shown by Calvert (1899) and united with 

 that of the metathorax, where it can be seen partially imbedded, 

 in the later stages. This causes the ganglion of the second seg- 

 ment to move forward into the first, leaving the second segment 

 A'acant in fully grown larvae and in adults. 



Tillyard (1917, page 132) states that he first discovered this fact 

 in the dissection of the adult Petalura, and adds that he thinks the 

 shifting must ''take place either before or during metamorphosis, 

 and is correlated with (a) the decrease in the size of the first ab- 

 dominal segment to a narrow ring, and (b) the great elongation of 

 the abdomen of the imago as a whole. " He further remarks upon 

 the stretching of the nerve cord in the adult and its supposed effect 

 in the location of the ganglia. • 



The dissection of a series of larvae, from those just hatched or 

 which have moulted but once or twice to those full grown, shows 

 that this shifting of ganglia comes about verj'' early in all groups, 

 certainly before any great changes in the proportions of the thorax 

 and abdomen have occurred. In fact, the change has alread}' 

 taken place before the larva is large enough to be dissected. 

 Such being the case it would seem to have little to do with the 

 elongation of the abdomen. 



A glance at the figure of Lestes (plate XXI, figure 1) shows that 

 the seven abdominal ganglia are all located in the extreme anterior 

 ends of their respective segments, with minor variations in the 

 third and eighth segments. The ganglion of tlie thiid has been 



TRANS. AM. ENT. SOC, XLIV. 



