Dorsal Vessel 



71 



nuclei, wliicli often project into the lumen of tlie tubule 



(%• 51)- 



The muscular wall of Deveiop- 



, , , . , 1 . meiit of 



the alimentary canal is striped 



11 'Jii ,^ ,1 muscular 



well suited to the study fibres, 

 of the development of 

 striped muscular fibres 

 from simple muscle- 

 cells. AYe have made 

 some progress with the 

 investigation, but found 

 it necessary to leave this 

 and many other special 

 features incomplete, in 

 order to bring our work 

 to a close in moderate 

 time. The valuable 

 Recherches of Viallanes 

 (1882) would be a useful 

 guide to any one who 

 might be disposed to 

 pursue the inquiry. 



5. The Heart and 

 Circulation. 



"When a live larva is Dorsal 



vessel. 



examined under the 

 microscope, the dorsal 

 vessel is easily seen on 

 the bach of the hinder 

 part of the body (fig. 39). 

 In Dipterous larvae the 

 parts — the heart, which 

 runs forwards from the 



Fio. 52. — Muscle-cells of larval alimentary 

 canal, i, optical sections of fresh oesopha- 

 geal muscle-cells, showing differentiation of 

 contractile substance. The same appearance 

 occurs in the intestinal muscle-cells ; some- 

 times it cannot be found. 2, striated con- 

 tractile substance and nuclei of muscle-cells 

 of oesophagus. 3, muscle-cells of intestine, 

 examined in blood of larva. 4, the same, 

 after the addition of acetic acid. 



dorsal vessel is divisible into two 

 is posterior, and the aorta, which 



