354 TEXT-BOOK OF ENTOMOLOGY 



found from 16 to 18, and in nymphs 4 to 5 mm. long there were only eight vessels ; 

 while Wheeler has found in the embryo of Phyllodromia germanica but four 

 tubes. In the adult Acrydiidae there are as many as 150, in the Locustidse 

 between 40 and 50, and in the Gryllidse about 100. 



The Ephemeridse with about 40, the Odonata with 50 to 60 tubules, the Per- 

 lidse with from 50 to 60, are polynephrious ; while the Termitidse and Psocidse 

 are oligonephrious, the former having from six to eight and the Psocidse only 

 four tubes. So also all the other orders not mentioned, except the Hymenoptera, 

 have few of these tubes. The Hemiptera, with none in Aphidse, a single pair 

 in the Coccidse, and two in all the rest of the order, have the fewest number. 



In the Neuroptera there are from six to eight, while in a larva, possibly that 

 of Chauliodes, Wheeler finds the exceptional number of seven. 



The closely allied order Mecoptera (Panorpid*), and also the Trichoptera, 

 agree with the Neuroptera (Sialis) in having six. According to Cholodkowsky. 

 all Lepidoptera have six of these vessels, except Galleria, which has but four. 

 He finds that in Tinea biselliella (also T. pellionella and Blabophanes rusticella} 

 the larva has six vessels, which, however, undergo histolysis during pupation, 

 a single pair arising in their stead. On this account he regards the primitive 

 number of urinary tubes as two, or a single pair, this return from six vessels in 

 the larva to two in the imago being considered a case of atavism. 



In the Coleoptera, the number of urinary tubes is from four to six ; in what 

 few embryo beetles have been examined (Doryphora, Melolontha), there are six 

 vessels, but in the embryo of Dyticus fasciventris, Wheeler has detected only 

 four, this number being retained in the adult. He thinks that in beetles in 

 general, a pair of vessels must be "suppressed during postembryonic develop- 

 ment, presumably in early larval life." 



In Diptera and Siphonaptera, the number four is very constant, there being, 

 however, a fifth one in Culex and Psychoda (Fig. 400.) 



The number of these vessels is very inconstant in the Hymenoptera, varying 

 from six (Tomognathus, an ant, worker) to 12 (Myrmica), and in Apis reach- 

 ing the number of 150. 



In the embryo of the honey-bee and wall-bee (Chalicodotna) , there are only 

 four ; we still lack any knowledge of the number in embryo saw-flies. 



The following is a tabular view of insects with few urinary tubes 

 (Oligonephria) and many (Polynephria). It will be seen that the 

 number has little relation to the classification or phylogeny, insects 

 so distantly related as the Orthoptera and Hymenoptera being 

 polynephrious : 



Oligonephria 



Colleinbola, 2 (Podura), Tullberg and 



also Sommer. 

 Thysanura, 4 (Lepisma); inCampodea, 



16 ; in Machilis, 12 or 20 ; wanting in 



Japyx. 

 Psocidse, 4. 

 Termitidse, 6 (many in the young, 



Rathke). 

 Mallophaga, 4. 

 Physapoda, 4. 



Hemiptera, 2 (Coccidse, none in Aphi- 



d). 

 Neuroptera, 6-8. (In Sialidse and 



Khaphididse, 6 ; in Myrmeleonidfe 



and Hemerobidse, 8). 

 Trichoptera, 6. 

 Mecoptera, 6. 

 Lepidoptera, 2-4-6 (2 in Tinea, Tineola, 



and Blabophanes ; in Pterophorus 



and Yponomeuta, 4). 



