SEGMENT A TION. 33 



Segments. — The integument is obviously divided by circular 

 sulci into a series of rings or segments. If the small head be 

 considered the first segment, the second, third, and fourth 

 obvious segments belong to the thorax, and the second bears a 

 pair of pedunculated spiracles. There are no spiracles on the 

 segments which intervene between this and the last, so that 

 this larva is amphipnciistic (see page 28). Each segment has a 

 thickened anterior border, covered by short recurved spines 

 and sensory papillae. The spines apparently prevent a retro- 

 grade movement in burrowing, like the setae of an earth 

 worm. 



The abdominal segments exhibit a dorsal and a ventral arch, 

 separated by a marked lateral fold, and the ventral arch is 

 divided by a transverse sulcus into an anterior and posterior 

 portion. 



Although it would appear at first sight perfectly easy to 

 count these segments, authors are by no means agreed as to 

 their number. Dr. Weismann [2] gives twelve, reckoning the 



Dipt{;res.' Mem. Pres. ?l I'Acad. des Sc. Math, et Phys., torn, xi., 

 pp. 171-360. II pi., 1851. 



20. Leuckart, R., ' Fortpflanzung und Entwicklung der Pupiparen.' 



Abh. Nat. Gesellsch., Halle, Bd. iv., 1S58. 



21. SCHEIEER, S. H., ' Vergleichende Anatomie und Physiologie der 



Ostriden-Larven.' Sitzungbericht der K. Akad., Wien. Bd. xli., 

 pp. 409-496, i860 ; and Bd. xlv., pp. 7-68, 1862. 



22. Leuckart, R., 'Die Larvenzustiinde der Musciden.' Archiv. f. 



Naturgesch. Jahrg. 27, 1861. 



23. Marno, Ernst, ' Die Typen der Dipteren Larven.' Verhand. der 



Zool. Bot. Gesellsch. in Wien. Bd. xix., 1869. 



24. Hammond, A., ' The Anatomy of the Larva of the Crane-fly.' Sc. 



Gossip, vol. xi., pp. 10, 171, 201. 1875. 



25. KiJNCKEL D'Herculais, Jules, ' Recherches sur I'Organisation et le 



Ddvcloppement des Volucclles.' Fol., Paris, 1S75-81. 



26. Batelli, Andrea, ' Contribuzione all' Anatomia ed Fisilogia della 



Larva dell' Eristalis tenax.' Bull, della Soc. Ent. Ital., 1879, 

 pp. 77-120, with 5 plates. 



27. VlAi.LANES, H., ' Recherches sur I'Histologie des Insectes et sur les 



Phdnom^nes histolyliqiie qui accompagnent lo ddvcloppement post- 

 embryonaire de res animaux.' Ann. Sc. Nat. Zool., ser. vi., tom. 

 xvi., pp. 1-348. l8 pis., 1882. 



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