Bodv-cavitv. Dorsal Vessel 



175 



Our information respecting; the development of the Body- 



. , Ti cavity. 



bodv-cavity and dorsal vessel is neither lull nor alto- Dorsal 



vessel. 



getlier trustworthy. Very few of our sections illustrated 

 the later stages of formation. The paired longitudinal 

 thickenings on the inner face of the ventral plate, 

 described on p. 163, become transversely segmented and 



hollow. The cavities soon 

 unite on either side to form 

 a coelom. Then the walls 

 of the mesenteron become 

 detached from the ridges, 

 as described on p. 163. 

 The ridges next begin 

 slowly to grow upwards 

 and to enclose both mes- 

 enteron and yolk. The 

 narrow body-cavity extends 

 of course at the same time. 

 The outer layer yields the 

 muscles of the body-wall, 

 while much of the inner 

 layer seems to break up, 

 perhaps into wandering 

 cells and blood-corpuscles. 

 From the dorsal margin of 



Fia. 129.— Larva coiled up within the the mesodermal layers are 



egg, jnst before hatcliing. Ir, labruni. -i • 1 j-l Tic. r\V ^■^ a 



ant, antenna, mcl, mandible, mx, max- CleriVeCl tllC liaiVCS 01 tlie 



ilia. J6, labium. 6r, brain (within the ,i „,,„„! -rraacAl 



head), p/, prothoracic foot, a./, anal "-lUibcii ve&&«i. 



f°°t- During the fifth day the Fifth day. 



head and jaws acquire very nearly their ultimate form. 

 The salivary glands and ducts, which had a separate 

 origin, now open into the mouth. The body is con- 

 siderably longer than the egg, and somewhat coiled, as 

 shown in fig. 128. 



On the sixth day, the coiling increases, and the larva sixth day. 



