NORTH AMERICAN ODONATA. 183 



pair supplies the muscles of its own segment; segment 2 is supplied 

 by branches from the first pair of ganglia, segments 9 and 10 and 

 the terminal appendages by the seventh pair. The experiments of 

 Barlow (10) Plateau (11) and others have shown that each pair of 

 abdominal ganglia is a respiratory centre for its own segment. The 

 high degree of independence of the rest of the nervous system pos- 

 sessed by the different parts is shown by the experiments of Stephens 

 (Ent. Mag. I, p. 518, 1833), who induced an Aeschna to devour its 

 own terminal four abdominal segments, and which then "fled away 

 as briskly as ever ;" by similar experiments of the writer on Pa- 

 chydiplax longipennis ; and by the continuance of respiration after 

 decapitation, or in portions of the abdomen consisting of three or 

 four segments which have been removed from the rest of the body, 

 as noted by Barlow. 



The termination of the motor nerves in the nymph of Libellula has been in- 

 vestigated by Gabbi, who finds that the sheath of the nerve enters into close 

 relations with the primitive muscle-bundle and is continued into the sarcolemma 

 which forms the so-called elevation of Doyere. The axis cylinder penetrates 

 the apex of the elevation of Doyere and divides into two branches at the base 

 of the cone. The motor termination is situated below the sarcolemma (Bull. 

 Soc. Ent. Ital. XVIII, pp. 310-333, 1886). 



Special Sense Organs. — The external features of the compound eyes have been 

 already referred to (p. 155), where the difference in size between the facets of 

 the upper and lower surfaces in the eyes of the Lihellulidse and Aeschniuaj was 

 mentioned. Exner finds that the separate facet-members of the upper surface 

 are absolutely, but not relatively longer, and possess no black pigment ; the re- 

 verse is the case in those of the lower parts, and the transition between the two 

 kinds in these respects is quite abrupt.® When the eyes of the living insect are 

 examined, a number of black spots are seen, which change their location as the 

 eye is looked at from various points of view; these are the " pseudopupillje." 

 Exner believes that the upper part of the eye is for "the perception of move- 

 ments, the lower for the perception of form of resting objects," a conclusion for 

 which he finds support in the fact that the pscudopupillae of the upper surface 

 move more rapidly, when the insect is turned in the hand, than do those of the 

 lower surface (Die Physiologic der facettirten Augen von Krebseu und Insecten. 

 Leipzig u. Wien, 1891). On the other hand, Plateau considers that the Odonata 

 do not perceive form, but merely motion (Bull. Ac. Belg. (3), XVI, pp. 417-425, 

 1888). 



Lespes describes (Ann. Sci. Nat. (4), IX, p. 240, 1858) certain structures on the 

 antennae which he regarded as auditory; in Agrion, on the third antenual joint, 

 he found an opening closed by a white membrane, and on the fifth four tympan- 

 ules placed in line, one above the other; in Libellula (Diplax) vnlgatu was nothing 



* Additional details on the histological structure of the eyes are given bj' 

 Lowne, Trans. Linn. Soc. (2) II. pp. 389-420, and Hickson, Quart. Journ. Micr. 

 Sci (n. s.) XXV, pp. 222-223, etc. 



TEANS. AM. ENT. SOC. XX. AUGUST, 1893. 



