APPENDAGES OF THE SECOND ABDOMINAL SEG- 

 MENT OF MALE DRAGON FLIES (ORDER ODONATA) 



BY 



OLIVER S. THOMPSON 



The appendages of the abdomen in male dragon flies are of 

 two sorts : those at the end of the abdomen, that are used for 

 capturing the female and leading or guiding her about, and 

 those on or adjacent to the sternum of the second segment, 

 that are used for copulation. The former are probably of more 

 ancient origin; the latter, more recently and secondarily ac- 

 quired. The former are capable of being homologized with like 

 parts in other orders of insects; the latter are not, being pe- 

 culiar to dragon flies. Both are of much use in the recognition 

 of species, for the ultimate specific differentiations are oftenest 

 found in these parts. 



The occurrence of organs for copulation upon the body at 

 points remote from the orifices of the sperm ducts is, of course, well 

 known in spiders, cephalopods, etc., and the origin of these 

 parts is always shrouded in mystery. In none would the begin- 

 nings be more difficult of explanation than in the Odonata. 

 Here the sperm ducts open on the ventral side of the 9th ab- 

 dominal segment : the copulatory apparatus is on the ventral 

 side of the 2d and 3d segments. Previous to copulation, the 

 abdomen is bent upon itself until the sperm orifice is brought 

 into contact with the sperm vesicle situated at the front of the 

 sternum of the 3d abdominal segment, and the vesicle is charged 

 with spermatozoa. The terminal abdominal appendages of 

 the male are used to seize the female. They grasp her by the 

 head or by the prothora:x, and by ventral flexion of the abdo- 

 men, swing her into an inverted position, so that her genital 

 orifice, situated on the ventral side of the 8th abdominal seg- 

 ment, may be brought into contact, not with that of the male, 

 but with the accessory apparatus developed upon the 2d 

 abdominal segment of the male. Thus the sperm is trans- 

 ferred. It is a rather remarkable process : how it started al- 

 most surpasses imagining. 



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