MUSEUM OF COMPAEATIVE ZOOLOGY. 153 



any time in the course of manipulation a change to a denser fluid be 

 made too suddenly, the result will be to force the partition forwai'd, and 

 consequently to bend the oesophagus in the space between the brain and 

 the partition, where it is free from supporting tissue. Exactly this is 

 shown to have happened, only in a less degree, in my Figure 8. 



Following now the course of the oesophageal cell after it emerges from 

 the partition into the general body cavity, one finds a second cell along- 

 side of it (Plate III. Fig. 33, cl. in. I.), which resembles it in the entire 

 absence of transverse cell boundaries and in the presence of many nuclei, 

 but is unlike it in the highly granular condition of the protoplasm and 

 in the shape and appearance of the nuclei. Since the intestine hangs free 

 in the body cavity, the position of the cells can be determined only in 

 a general way. The new cell, which may be named the first intestinal 

 cell, lies approximately lateral to the oesophageal cell (Fig. 33). It be- 

 gins at about 0.8 mm. from the apex of the head ; about 0.4 mm. far- 

 ther back, a second intestinal cell (cL in. II., Fig. 34) is added. This 

 lies nearly ventral. A third cell (cl. in. III., Fig. 35) begins 1.3 mm. 

 from the apex of the head, and a fourth [cl. in. IV., Fig. 36) 0.1 mm. 

 farther posteriad. This completes the number. The oesophageal cell, 

 which may be recognized by the presence in it of the cross section of 

 the chitinous tube, now lies lateral to the four intestinal cells (Fig. 36), 

 but soon wedges itself in between two of them until it reaches the centre 

 of the group (Fig. 43), and then suddenly ends, leaving a cavity (Fig. 44) 

 surrounded by the four intestinal cells which have accompanied it a 

 longer or shorter distance from their origin. 



It is now necessary to ask how the chitinous tube is concerned in these 

 changes. Up to the point where the fourth intestinal cell is added, it 

 remains a straight simple tube. Shortly beyond that point it makes a 

 complete turn upon itself (Plate I. Fig. 8), and from a lateral position 

 with reference to the four intestinal cells it reaches a median one 

 (Plate III. Figs. 37-43). Hence the loop lies in that portion of the 

 oesophageal cell which is wedged in between two of the intestinal cells 

 (Fig. 38), and almost completely fills the space. The tube proceeds 

 a short distance farther, 60 [x only, tapers to an exceedingly fine point, 

 and opens out into the space which has arisen between the four intes- 

 tinal cells (Figs. 8 and 44). This space is the intestine proper, and 

 justifies the application of the name " intestinal cells" to those elements 

 which, though originating farther forward, were destined to bound it. 

 These relations, which are evident in every complete series through this 

 region, are represented in a succession of figures taken from one series of 



