SEGMENTA 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 amphipncustic (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 



Dipteres.' ]\Iem. Pres. a I'Acad. des Sc. Math, et Phys., torn, xi., 

 pp. 171-360. II pL, 1 85 1. 

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

 Abh. Nat. Gesellsch., Halle, Bd. iv., 1858. 



V 21. SCHEIBER, S. H., ' Vergleichende Anatomic und Physiologic dcr 

 Ostriden-Larvcn.' 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 Larvcn.' Verhand. der 

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



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

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



25. KUNCKEL D'Herculais, Jules, ' Rccherchcs sur I'Organisation et le 

 Developpement des Volucelles.' Fol., Paris, 1875-81. 



V 26. Batelli, Andrea, ' Contribuzionc all' Anatomia ed Fisilogia della 

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

 pp. 77-120, with 5 plates, 



27. VlALLANES, H., 'Recherches sur I'Histologic des Insectes et sur les 

 Phenomenes histolytique qui accompagnent le developpement post- 

 embryonaire dc ces animaux.' Ann, Sc. Nat. Zool., ser. vi., torn, 

 xvi., pp. 1-348. 18 pis., 1882. 



