NORTH AMERICAN ODONATA. 173 



fulcral process. The depressor muscles are to the outside of the 

 elevators, while their insertions lie xvithout the plane of the fulcral 

 process. Elevation of the wing is by the operation of a lever in 

 which the fulcrum lies between the points of application of the 

 power and the weight, but close to the former. In depression of the 

 wing, the fulcrum is at one end of the lever, the power being ap- 

 plied near to, but outside it. Lendenfeld (4) has determined the 

 total weight and the area of the wings of some European Odonata 

 as follows, from which the relative wing area per .1 gram, has been 

 ascertained. 



Rel ative wing 

 _ ^ . . Total area of wings area in square 

 lotaJ weight in square centi- centimetres per 

 in grammes. metres. .1 gram, of body 



weight. 



Aeschna cyanea '^ 92 11.45 1.2445 



Libellula cancellata 'S 44 7.04 1.6 



Libellula quadrimacnlata % 29 5:54 1.91 



Agriou puella 026 1.10 4.23 



Calopteiyx Virgo "J, 1 5.56 5.56 



Ramon y Cajal found (Intern. Monatschr. Anat. u. Phys. v, p. 267, 1888) the 

 nuclei of the wing muscle fibres to be central, large, and elongated ; cross-sections 

 showed radiations from the nucleus to the sarcolemma. In the fibres of the leg 

 muscles, the nuclei are peripheral. Some additional details by the same author 

 are contained in Zeit. Wiss. Mikros. vii, p. 335, 1890. 



Muscles of the Front Wings : 



Anterior depressor of the front wings (abductor alse primse Lendenfeld, abaisseur 

 anterieur Poletaiew) rises on the anterior part of the mesinfraepisternum and 

 the lower part of the mesepisternum ; it inserts by a cap-tendon into the ante- 

 rior axillary callus a little in front of the costa and of the fulcral process. Len- 

 denfeld states that this muscle is "extraordinarily feeble in Calopteryx ;" it is 

 not so in C. maculata. 



Accessory of the anterior depressor (pronator radii primi Lend., additionnel au 

 abraisseur anterieur Pol.), a very small muscle, arises from the lower part of the 

 mesepisternum near the infraepisteruum, and lies upon the middle of the outer 

 side of the anterior depressor; at about one-third its length the belly passes into 

 a slender cap-tendon, which inserts close to and on the outer side of the inser- 

 tion of the anterior depressor. 



Posterior depressor of the front wings (flexor alfe primse Lend., abraisseur pos- 

 terieur Pol.) rises from the hind part of the mesinfraepisternum and the lower 

 part of the mesepimeron, and inserts by a cap-tendon into the pleural membrane 

 of the base of the wing, below the median vein. 



First accessory of the posterior depressor (additionnel posterieur au abaisseur 

 posterieur Pol.), a small muscle, lies on the outer and hinder side of the posterior 

 depressor, arising from the metepisternum just behind the apodeme of the rudi- 

 mentary first lateral suture and above the origin of the accessory of the anterior 

 depressor of the hind wings: it inserts by a very slender tendon into the wing- 

 base below the post-costa. 



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



