28 THE DEVELOPMENT OF 



a well marked tube in all of the anterior transverse sections 

 of stage H (figs. 57, 59, 60, 62-65, d). The superior ab- 

 dominal artery is much less marked, while neither in the 

 living embryo nor in my sections have I seen traces of other 

 arteries than these. In view of the fact that in the adult 

 the ophthalmic artery is the smallest of the five arising di- 

 rectly from the heart, its prominence at this stage seems 

 strange until we consider that the hepato-gastric and ster- 

 nal arteries would have to supply regions which at this time 

 are charged with food yolk, while the enormous eyes are 

 far removed from the deutoplasm and must have all nour- 

 ishment brought them from a distance. 



CEPHALIC MESODERM. The mesoderm, which in stage 

 C had extended itself into the region in front of the mouth, 

 remains comparatively unmodified until about stage F. In 

 the median line (figs. 42 and 43 m) it appears as a moderate 

 patch extending in the former down between the ganglia. 

 A better view of its extension can be gained in fig. 48, 

 where, in the median line, it is a thick mass sending out a 

 narrow sheet on either side, from which a strand stretches 

 upwards, while another goes outwards and downwards (as 

 shown by fig. 49, taken from the same embryo five sec- 

 tions farther back) into the region of the first and second 

 antennae. In stage H the central patch is largely utilized 

 in forming the muscular wall of the oesophagus, while the 

 lateral portions (figs. 55-61) retain about their former po- 

 sition, but send (figs. 56, 57 and 58) a band between 

 the ommatidial elements and the optic ganglion. It is to 

 this layer that I referred in my preliminary account of 

 the compound eye of Crangou('86a)as intruding between 

 the ommatidial and gangliouic layers and giving rise to the 

 intrusive mesodermal pigment surrounding the nerve fi- 

 bres in that region. 1 did not and do not regard this as 

 in any way giving rise to the pigment surrounding the 

 pedicels, which clearly arises from the ectoderm. 



