'202 PHILIP p. CALVERT. 



by Hagen (-7). Dufour (L c.) regarded the caudal tracheal-gills 

 of Calopteryx merely as " swimmerets or oars," and although they 

 do serve this purpose, yet the middle tracheal-gill is well supplied 

 with tracheals and apparently functions as a respiratory organ. The 

 nymphs of the Calopterygine genus Euphoea are remarkable in that 

 they possess three functional caudal tracheal-gills, three rectal tra- 

 cheal gills, and an external, conical tracheal-gill on each side of the 

 first eight abdominal segments (Hagen 52). 



The thin caudal tracheal-gills of the Agrioninse are well supplied 

 with trachese, but as the nymphs live after these are removed, Dewitz 

 (25) suggests that here also the rectum may perform respiratory 

 functions. No rectal tracheal-gills, however, have been found as 

 yet in this subfamily, although the rectal walls are well supplied with 

 trachere. 



There are ten pairs of spiracles, as in the imago, and similarly 

 distributed. They are all open, but those of the abdomen are prob- 

 ably not functional (Hagen 27, 52). The thoracic stigmata become 

 functional at an earlier period in the nymphal life of the Agrionidse 

 and Libellulidse than of the Aeschnidse, but in all three cases only 

 on one side of the body (Dewitz 25). 



The nerve-ganglia occupy the same i)ositions in the old nymphs as 

 in the imago. In a Libelluline nymph, genus unknown, the writer 

 found the meso- and metathoracic ganglia distinct, although nearer 

 to each other than the former to the prothoracic pair ; the san)e 

 nymph had the testes well-developed. While each of the first eight 

 abdominal segments of the young nymphs of hchmra verticalis and 

 Libellula pulchella has a pair of ganglia, all old nymphs, as far as 

 known, have seven pairs as in the imago. In what way the reduc- 

 tion is effected is unknown, but the result is to leave the second ab- 

 dominal segment without ganglia of its own (see p. 188). 



The nymphs are ordinarily not very active, although when dis- 

 turbed they can move quite rapidly, those of the Zygoptera by a 

 serpentine movement of the abdomen, those of the Anisoptera by a 

 series of "jerks," propelled by the water ejected from the rectum. 

 Most of this period is spent clinging to the under surface of plants, 

 sticks and stones, relying on a cautious approach and a sudden move- 

 ment of the mask to obtain their living food.* 



The food of the nymphs has already been considered in connection with the 

 alimentary canal of the imago, p. 177. 



