Fig. 222. A. Larva of Eurylepta auriculata immediately after hatching. Viewed from the side. (After Hallez.) m. mouth.
B. Müller’s Turbellarian larva (probably Thysanozoon). Viewed from the ventral surface. (After Müller.) The ciliated band is represented by the black line. m. mouth; u.l. upper lip.
The præoral lobe is usually the seat of a special thickening of epiblast, which gives rise to the supraœsophageal ganglion of the adult. On this lobe optic organs are very often developed in connection with the supraœsophageal ganglion, and a contractile band frequently passes from this region to the œsophagus.
The alimentary tract is formed of the three typical divisions.
The body cavity is not developed directly as an outgrowth of the alimentary tract, though the process by which it originates is very probably secondarily modified from a pair of alimentary outgrowths.
Paired excretory organs, opening to the exterior and into the body cavity, are often present ([fig. 226] nph).
This type of larva is found in the Rotifera ([fig. 217]) (in which it is preserved in the adult state), the Chætopoda ([figs. 225] and [226]), the Mollusca ([fig. 218]), the Gephyrea nuda ([fig. 227]), and the Polyzoa ([fig. 228])[140].
