41 8 MORGAN. [Vol. V. 



The oesophagus of a larva of this stage has been shown in 

 cross-section in Fig. 33. Its connection with the stomach is 

 now shown in longitudinal section in Fig. 37. A distinct groove 

 marks the point of union, and the section shows a gelatinous-like 

 secretion filling the groove at gr. The cilia on the dorsal wall (d) 

 of the oesophagus do not continue into the stomach, while those 

 over the ventral side continue, after a slight interruption at the 

 groove, as a narrow band down the anterior wall of the stomach ; 

 the cilia become smaller as the band runs down the wall, and 

 cease about the middle of the stomach. The cells forming the 

 stomach wall in this region are higher than elsewhere, as shown 

 in cross-section by Fig. 38. This band of cilia is also found in 

 other species of Tornaria, and seems to be a distinctive feature of 

 the larva. The gill pouches arise as evaginations from the upper 

 part of the oesophagus. Three pairs appear in this larva almost 

 simultaneously, but the first is larger than the second, and the 

 second than the third. A fourth pouch arises just prior to the 

 transformation of the larva, and at this time the first one or two 

 develop the tongue bars. Fig. 8, PI. XXIV., shows a view of 

 the dorsal surface of the oesophagus of the larva shown in Fig. 6. 

 The left side is an optical section, and the right a surface view. 

 The oesophagus is exceedingly broad, and the pouches arise from 

 the upper outer corners. 



The apical plate of the larva, is shown in surface view by 

 Fig. 7, PI. XXIV. To obtain this, the upper part of the larva 

 was dissected away, mounted in glycerine, and stained in methyl 

 green, which brings out distinctly the course of the ciliated 

 bands. Each of these four bands is clearly seen to end sharply 

 in the region of the apical plate, with the points turned in from 

 right to left, and left to right, the anterior two pointed towards 

 each other, and the more posterior likewise toward each other. 

 The earlier stages of these bands (as shown in Fig. 4) showed 

 no such breaking in their course, but were simply continuous 

 with the thickened ectoderm of the apical plate. I have 

 assumed in their earlier stages that the ciliated bands are con- 

 tinuous over the apical plate, across the sides, so that there 

 is a single circumoral band. However, in the older stages, as 

 seen in Fig. 7, this is not the case, but there is a tendency to a 

 separation of the circumoral band into two separate bands, the 

 one above and anterior to the mouth, and the other if the bands 



