320 SYNOPTIC COLLECTION. 



10). The very young larva (fig. i, dorsal view; fig. 2, 

 ventral view) is provided with eye-spots and ciliated lobes. 

 The body and lobes increase in size, and the larva (fig. 3, 

 dorsal view; fig. 4, ventral view) is found swimming 

 freely at the surface of the sea. The body elongates (fig. 

 5, dorsal, and fig. 6, ventral view), and the lobes begin 

 to be resorbed (fig. 7, dorsal, and fig. 8, ventral view). 

 Finally by the suppression of the lobes, the young sexual 

 form (fig. 9, dorsal, and fig. 10, ventral view) resulting 

 from the metamorphosis is produced. This form is 

 essentially like that of the adult. 



The broad, flat, marine Leptoplana gigas Schm. (No. 

 791, model), has, like Thysanozoon and most of its group, 

 an unsegmented body with the mouth near the center of 

 the ventral side. The digestive system is extremely com- 

 plicated, as shown by PI. 792, L. alcinoi. The central 

 stomach gives off intestinal branches which fill the body 

 cavity and end blindly, there being no anus. These ani- 

 mals are often called solid-bodied worms and are con- 

 trasted with the hollow-bodied forms, such as the Chaeto- 

 pods, Nematodes, and the like. 



Among the Triclad marine Turbellaria, Planar ia angu- 

 lata is interesting since it differs from most of its class 

 by having a segmented cylindrical body (PL 793, figs, i, 

 2) which in the course of development loses its segments 

 and becomes flattened. 



A fresh-water Triclad Turbellarian, Planaria lactea 

 Baer (No. 794, model), is a flat and nearly transparent 

 worm. Extending down the back is the digestive system 

 which is characteristic of the Turbellaria, as we have 

 already shown. It consists in this genus of a median 

 tube which gives off two branches. Near the middle of 

 the body this median tube divides into two large branches 

 which extend backward giving off smaller branches. At 

 the point where the median tube divides there is a good- 

 sized bag, the proboscis, which seizes the food. As in 

 the Polyclads, the intestine in the Triclads ends blindly, 

 there being no anus. 



