ANATOMY AND PHYSIOLOGY 



IIQ 



FIG. 173. Caudal 



it. These adaptations are often supplemented by waving movements of 

 te gills, as in May fly nymphs, and by frequent movements of the 



isect from one place to another. 

 Especially noteworthy are the rectal trac heal gills of odonate nymphs. 



[n these insects the lining of tJie~"~rectuni forms numerous papillae or 

 lamellae, which contain a profusion of delicate tra- 

 cheal branches; these are bathed by water drawn 

 into the rectum and then expelled, at rather irregu- 

 lar intervals. A similar rectal respiration occurs 

 also in ephemerid nymphs and mosquito larvae. 



A i . n n TJ ;_ i gills of a damsel flv 



few forms, chiefly Perlidae, are exceptional in nympht enlarged. 



retaining tracheal gills in the adult stage; in some 

 imagines they are merely vestiges of the nymphal gills, but in others, 

 such as Pteronarcys (Fig. 19), which habitually dips into the water 

 and rests in moist situations, the gills probably supplement the spiracles. 

 Further details on the respiration of aquatic insects 

 are given in Chapter IV. 



Blood-gills. In a few aquatic larvae, Simulium 

 and Chironomus for example, there are thin tubular 

 evaginations of the integument known as blood-gills, 

 into which the blood flows. In trichopterous larvae 

 (caddis- worms) the blood-gills are eversible. Some 

 authors regard the ventral eversible sacs of Scolo- 

 pendrella and Thysanura, as well as the vesicles of 

 the ventral tube of Collembola, as blood-gills. 



Spiracles. The paired external openings of the 

 tracheae, termed spiracles or stigmata, occur on the 

 sides of the thorax and abdomen; there being not 

 more than one pair to a segment, though not all 

 segments bear them. As a rule, there are two tho- 

 racic and eight abdominal pairs; these belonging to 

 the mesothorax, metathorax, and first eight abdom- 

 il segments, respectively. Adult insects do not 

 have more than ten pairs, with the exception of 



. ? \ 



Japyx (see page 60, footnote) . 



The spiracles, variable in position, are situated usually between two 

 segments of the body; but often at the anterior borders of the seg- 

 ments to which they belong; though they may occur farther back on 

 the segments. 



In most embryo insects there are eleven pairs of spiracles three 



FIG. 174. Cater- 



to P showTra- 

 cheal gills. Length, 15 



mm. After HART. 



