No. 3.] GROWTH AND METAMORPHOSIS OF TORN ARIA. 409 



much of the interior of the larva. The walls are thin, however, 

 without any trace of yolk in them. The stomach is separated 

 from the posterior (endodermic) portion of the digestive tract — 

 "the intestine" — by a diaphragm-like partition. The partition 

 is pierced in the centre by a small opening, not seen in the 

 figure, richly supplied with long cilia, so that the stomach and 

 intestine are placed in communication. Posteriorly the intes- 

 tine opens by an anus. Near the mid-dorsal line above the 

 intestine lies a small vesicle, shown in Fig. 2, with flattened 

 epithelial wall communicating with the exterior by a small pore 

 somewhat in the left of the middle line. This is the anterior 

 (unpaired) enteroccel, e, and is shown on a larger scale in Fig. 4. 

 In the latter figure the flask-shaped enteroccel is seen lying upon 

 the stomach (the cell walls and nuclei of the latter are seen), 

 and the flattened cells forming the walls of the enteroccel are 

 seen to become more columnar on the walls of the tube which 

 opens to the surface by the water pore. There is no connection 

 whatever in an embryo of this age between the cavity of the 

 anterior enteroccel and that of the digestive tract. In Fig. 1 

 there is seen to be a thin band of a muscular nature run- 

 ning upwards from the enteroccel to the apical plate at mb. 

 Goethe has figured a very young embryo of Tornaria, and the 

 figure has been widely copied. He shows a large pouch run- 

 ning out from the oesophagus, and calls this the earliest stage in 

 development of the water system. The pouch has columnar 

 cells forming its walls, and lying above it is a mass of flattened 

 cells which he does not name. The latter are, however, I 

 believe, the true enteroccel, and the evagination merely an 

 artifact due to a fold in the oesophageal walls. The indis- 

 tinctness of the lower wall connecting the enteroccel with the 

 digestive tract indicates this, and the relation of the small mass 

 of cells lying above the artifact, to the muscle band points to 

 its own identity with the water system. 



The path of the ciliated bands may be gathered from the 

 figures. In general, we may say there are two bands present 

 in such an embryo. The more anterior band, lb, I shall speak 

 of as the longitudinal or circumoral band. The posterior band 

 may be spoken of as the circular, cb. The longitudinal band may, 

 I think, at this stage, be spoken of as a single band having a 

 more or less sinuous course over the ventral (towards the oral 



