No. 3.] GROWTH AND METAMORPHOSIS OF TORN ARIA. 415 



the comparison between the various parts may be readily seen. 

 The most prominent difference between the two consists largely 

 in the more complicated foldings of the longitudinal ciliated 

 bands. This is especially marked in what I shall speak of as 

 the anterior lateral fold (ac) and the posterior lateral fold (be), 

 shown in Fig. 6. These are now much more marked than in 

 Fig. 5, extending farther posteriorly. Along the course of the 

 ciliated bands are to be seen large yellow-brown pigment spots. 

 The circular band, which is now very conspicuous, has also large 

 pigment spots along the lower edge posterior to the cilia. At 

 A is seen, in side view, the thickening of the apical plate. 

 Beneath the surface is seen the large digestive tract. The 

 mouth (m) leads into an oesophagus, which is broad from side 

 to side (see Fig. 8). Along the upper walls of the oesophagus, 

 in that part nearest to the stomach, are seen on each side (only 

 one side in the figure) three large gill pouches. The oesophagus 

 opens into the large stomach, the latter is followed by a large 

 intestine from which it is separated by a fold in the gut walls, 

 and the intestine opens at n to the exterior. Lying upon the 

 upper posterior part of the stomach is the large anterior entero- 

 ccel with its water pore near the mid-dorsal line. It is at a stage 

 of development shown in PI. XXV., Fig. 18. A conspicuous 

 muscle band runs from the upper end of the enteroccel to the 

 under surface of the apical plate. At be 2 and be 3 are seen the 

 two large paired enteroccels which nearly encircle the digestive 

 tract. The posterior lies about the level of the septum between 

 stomach and intestine ; and the more anterior paired enteroccel 

 is just in front of this, and separated by a narrow depression 

 from the posterior. 



A series of sections through the larva will show the relation 

 of the various internal organs. Three of these are given in 

 PL XXVL, Figs. 33, 34, 35. The first of these (Fig. 33) passes 

 below the mouth, cutting the oesophagus and water system. 

 On each side the longitudinal ciliated band is cut seven times. 

 The ectoderm is thickened at the ciliated bands, and its 

 nuclei stain more deeply. The area enclosed within the ante- 

 rior band — the circumoral area — is very thin in section, as seen 

 at x, y, and z, but with the exception that just below the mouth 

 the ectoderm is thicker (m') than elsewhere in the circumoral 

 area, and ciliated. In the mid-dorsal line the ectoderm is quite 



