DISTRIBUTION OF THE TRACHEAE 



435 



in the larvfe of Corethra and Chironomus the tracheal system is only incom 

 pletely developed ; the tracheae are not united with each other, and in the young- 

 est larvae they do not contain air. 



Each of the two main tracheae, as Kolbe states, 

 sends off into each segment of the body three 

 branches. 



1. An upper or dorsal branch, which supplies the 

 muscles of the dorsal region. 



2. A middle (visceral) branch, whose twigs pass 

 to the digestive canal and back to the organs of 

 reproduction. 



3. A lower (ventral) branch, whose twigs are 

 distributed to the ganglia and to the muscles of the 

 ventral region. 



In certain Thysanura, as a species of Machilis 

 (Fig. 397), we probably have the primitive condition 

 of the tracheal system, the longitudinal and trans- 

 verse anastomoses being absent, but in other Thy- 

 sanura (Japyx, Nicoletia, Lepisma, and a few species 

 of Machilis) they are present. 



As Kolbe remarks, whether the fine ends of the 

 tracheae are closed or open, whether after the analogy 

 of the blood capillaries of vertebrates they anastomose 

 with each other, whether the ends of the air-tubes 

 pass between the cells or penetrate into them, these 

 questions are not fully settled. According to Ley- 

 dig's 1 latest views the tracheae penetrate into the cells 

 and unite with the hyaloplasma. Hence the process 

 of respiration in the last instance takes place in the 

 hyaloplasma. This assumption accords with the fact 

 that in the tracheate Arthropods the terminations of 

 the trachepe carry the atmospheric air into the space 

 bounded by the cellular network, also to the hyalo- 

 plasma filling the spaces. Leydig 2 also thinks that 

 the finest tracheal endings penetrate into the muscular FIG. 397. Tracheal system 

 tissue and unite with the primitive muscular fibres. martma^Vhead' l / 'l'l / 'lll'* 



thoracic segments ; 1-1(1, ab- 



Kupffer is likewise of the opinion that the dominai segments; , stigma. 



After Oudetuans, from Lang-. 



fine tracheae penetrate into the cells, and Lidth 



de Jeude asserts that they enter the epithelial cells, "each cell con- 

 taining several branches." Kolliker, Emery, etc., maintain, how- 



1 Untersuchungen zur Anatomie und Histologie der Tiere, 1884, p. 72. 



2 Zelle und Gewebe, 1885, p. 43. (See also our p. 217.) 



FIG. 395. Mela nap? ux fern ur-rn/inim, showing distribution of air-tubes (trachea-) and air-sacs ; 

 I' main ventral trachea (only one of the two shown) ; S, left stigmatal trachea, connecting by vertical 

 branches with 1>, the left main dorsal trachea; c, left cephalic trachea ; oc, ocular dilated trachea. 

 From the tirst. second, third, and fourth spiracles arise the first four abdominal air-sacs, which are 

 siirrrcilcil by the plexus of three pairs of dilated trachea', I. II, III, in Fig. 396. Numerous air-sacs 

 and trachea- are represented in the head and thorax. The two thoracic spiracles are represented, 

 but not lettered. 



FIG. 39fi. D, left dorsal trachea; S t left stigmatal trachea; I, II, III, first, second, and third 

 pairs of abdominal dilated trachea?, forming a plexus behind the ovaries; 1, pair of enormous 

 thoracic air-sacs; '1, pair of smaller air-sacs; 3-7, abdominal air-sacs; tic, ocular dilated trachea 

 and air-sacs ; <. cephalic trachea. The relations of the heart to the dorsal tracheae are indicated. 

 Drawn by Eruerton from dissections by the author. 



