THE CANADIAN ENTOMOLOGIST. 245 



the false stigmata. The two remaining pair are situated, that of the 

 second segment on the longitudinal lateral abdominal seam, and that of 

 the first near the prothorax. All but the first pair of these spiracles, 

 although connected with the stem-trache» by branches, appear to be 

 rudimentary and nonfunctional, being merely an irregular slit in the 

 integument. The second pair can be recognized from the inside only, by 

 the tracheal connection, but there is no apparent opening. The so-called 

 stigmata of the third, fourth and fifth abdominal segments have no 

 appare7it co?inection with the tracheal system. I have demonstrated this 

 in several dissections by isolating the respiratory system m situ, and 

 following the branch tracheae to their termination in the body-wall. These 

 branches lead to the thickened wide border surrounding the sieve-like 

 portion of the false stigmata, which broadens on the inner side to accommo- 

 date the true slit-like rudimentary spiracle, to which the trachea can 

 clearly be seen attached. The late Joanny Martin^^ has followed the 

 development of these in the nymphal Nepa, and finds that they are 

 formed independently of the true functional stigmata of the nymph, which 

 at the last moult are narrowly obliterated. What the present function of 

 these peculiar structures may be is rather obscure, although it is possible 

 that they may be useful in aerating the body fluids by extracting oxygen 

 from the water by osmosis The structure of these stigmata in Nepa is 

 well shown in Dufour's work cited on the anatomy of the Hemiptera, figs. 

 194 to 200. 



Returning to the respiratory system, we find on the upper side of the 

 metathorax, under the wings, a large functional spiracle, which connects 

 by an ample trachea with the main system. This Schiodte calls the 

 " spiracula metathoracica." Further along we come to his " spiracula 

 mesothoracica," the second thoracic, which is smaller, and lies in the seam 

 between the meta- and mesothorax, concealed by the mesothoracic 

 epimera. The first pair of thoracic spiracles, which no other author 

 appears to have recognized, are situate at the cephalic margin of the meso- 

 thorax, in the membrane connecting it with the prothorax, and covered by 

 the latter. This pair is Schiodte's " spiracula prothoracica." They are 

 the largest spiracles in the insect, and are peculiar because of their oblong 

 rectangular shape, with rounded corners, and because they open not at 

 the end of a trachea, but in the wall of a large tube, which is here parallel 

 to the mesothoracic cephalic margin. The function of this spiracle is 



12. "Origine et formation desfaux stigmates chez les Xepidge (Hemipteres)." 

 Bull. Mus. de Hist. Xat., Paris, No. 3, pp. 1-2 (1895). 



