178 



PHILIP P. CALVERT. 



it has frequently been remarked by those who have reared them in 

 captivity, that the nymphs devour nymphs of their own and of other 

 species. Stefanelli observed the nymphs of the European Aeschna 

 cyanea to come out of the water at night and attack and devour the 

 newly-transformed imagos of the same species. Miss Wadsworth 

 has seen an imago of Dromogoviplms spinosus devouring an imao-o 

 of Calopteryx maculata, and Kuthy records Brachyiron pratense 

 preying on Somatoeldora flavomaculata. 



The excretory organs fire appendages of the alimentary canal. 

 They are known as the Malpjighlan tubules, and, as already men- 

 tioned, are attached to the point of junction of mid- and hind-gut. 

 Their number is from 50 to 70. The fullest account of them is by 

 Griffiths (8) for the European Platetrum depressum. In this species 

 they are 60 to 70 in number and unbranched ; each consists, fron) 

 without inwards, of " a connective tissue layer, a delicate tiacheal 

 tube, a basement membrane, and lastly an epithelial layer of com- 

 paratively large nucleated cells." The cavity of the tubule is very 

 irregular. The secretion of the tubules yielded uric acid, and no 

 other ingredient was detected. 



THE CIRCULATORY APPARATUS. 



The circulatory apparatus, so far as it has been recognized in the 

 Odonata, consists of a dorsal vessel of extreme tenuity, lying in the 

 abdomen above the alimentary canal and extending into the thorax. 

 Blanchard states that its openings are hardly visible and not marked 

 by constrictions; he counted seven pairs in Gomphus (Ann. Sci. 

 Nat. 1848, Zool. ix, p. 389). In the hind part of the dorsal vessel 

 of some Odonata are unstriated muscle fibres which are described by 

 Vosseler.* A ventral abdominal pulsating sinus is also recognized 

 by Graber. 



In close connection with the dorsal vessel and with the abdominal 

 ti'achese, are masses of yeUov,' fat, to which Graber assigned the func- 

 tions of absorption and the conveyance of nutrition to the various 

 organs ("Die Insekten," vol. I). 



THE RESPIRATORY APPARATUS. 

 The respiratory apparatus consists of three pairs of main longitu- 

 dinal trachea? with tlieir branches. The three pairs are found as 

 such only in the abdomen, where, from their position, they are termed 

 ventral, visceral and dorsal. 



■•■ Untersiichniigen iiber glatte und uiivollkoiumeu queigestreifte Muskeln der 

 Artliropodeu. Tubiugeii. 1891. Pp. 94-95. 



