XIX 



MAY-FLIES 



435 



VJ 



%W 



Fig. 280. Prosopi- 

 stoma pimctifrons, 

 nymph. France. 



(After Vayssiere.) o. 

 Orifice of exit from 

 respiratory chamber. 



of other Ephemerid nymphs. This pomt and other details 



of the anatomy of this creature have been 



described in detail by Vayssiere.-^ These 



nymphs have a very highly developed tracheal 



system ; they live in rapid watercourses 



attached to stones at a depth of three to six 



inches or more under the , water. Species of 



Frosopistoma occur in Europe, Madagascar, 



and West Africa. 



According to Eaton,^ in the nymphs of 



some Ephemeridae the rectum serves, to a 



certain extent, as a respiratory agent; he con- 

 siders that water is admitted to it and ex- 

 pelled after the manner we have described in 



Odonata, p. 421. 



The internal anatomy of the nymphs cf 



Ephemeridae shows some points of extreme 



interest. The long 

 caudal setae are 



respiratory organs of a kind that 

 is almost if not quite without 

 parallel in the other divisions of 

 Insecta. The dorsal vessel for the 

 circulation of the blood is elongate, 

 and its chambers are arranged one 



Fig. 281.-A, Last three abdominal * each segment of the body. It 



segments and bases of the three drives the blood forwards in the usual 



caudal processes of Cloeon dip- i ^ ^i, ^ i, i, 



^er^m; r, dorsal vessel ;H,ostia manner, but the posterior chamber 



thereof ; ^^ special terminal cham- posSCSSCS three blood-VCSScls, One of 



ber of the dorsal vessel with its , . , . , i , i it 



entrances; ^>, blood-vessel of the which IS prolonged into each caudal 

 left caudal process; B, twenty- geta. This terminal chamber is so 



sixth joint of the left caudal pro- i i i i i i 



cess from below ; 6, a portion of arranged as to dnvc the blood back- 

 the blood-vessel ; o, orifice in the ^y.^^^jg into the vessels of the sctae : 



latter. (After Zimmermanu.) . 



on the under surface of the vessels 

 there are oval orifices by which the blood escapes into the 

 cavity of the seta so as to be submitted to the action 

 of the surrounding medium for some of the purposes of 

 respiration. This structure has been described by Zimmer- 



i Ann. Sci. Nat. Zool. (7) ix. 1890, pix 19-87, pis. 2-5. 

 2 Ann. Nat. Hist. (3) xviii. 1866, p. 145. 



