Comstock and C. Kochi believe that the labrum belongs to it,, The appendages of the posterior three or trophal segments become the parts of the mouth.
Heymons considers that it represents the sternites of the three trophal segments, and that the gula is merely a secondary development.
The nervous system of the embryonic head exhibits three ganglionic masses, anterior to the thoracic ganglionic masses; these three masses subsequently amalgamate and form the sub-oesophageal ganglion, which supplies the trophal segments.
How would you define trophal? Add your definition here.