26 BULLETIN OF THE 



of the others; thus in Figure 61 its tip is cut, in Figure 60 there are 

 only 14 tentacles visible, and these are found in the two following sec- 

 tions. Since there are six sections which pass through the tentacles, 

 and the odd tentacle is found in only three of these, it follows that it 

 is only about one half as long as the others. 



The nervous system arises, as in PhylactolaBmata, by a depression in 

 the floor of the common atrio-pharyngeal cavity, in the region which later 

 becomes the anal surface of the pharynx. As in Phjdactolaemata, we 

 first see a shallow pit (Fig. 25, gn.). This appears to become deeper, 

 sinking downward and somewhat toward the cardiac valve (Fig. 7S, gii.). 

 Finally it becomes constricted off from the wall of the oesophagus, and 

 then appears as a cellular mass closely attached to it and surrounded 

 exteriorly only by mesoderm. (Plate I. Fig. 8 ; Plate VI. Figs. 52, 

 53, ffu.) Even before the closure of the ganglionic pocket is completed, 

 the formation of the circumcesophageal nerve, first described by Krae- 

 pelin ('87, pp. 62, 63) in the adult, begins. 



Figure 52 (Plate VI.) shows a transverse section of a young polypide 

 in which the ganglion is solid, and not provided with a large cavity as 

 in Phylactolsemata. There is a small cavity in the upper part of the 

 ganglion, and this is not yet wholly closed from the oesophagus. The 

 ganglion is continuous with a pair of hornlike processes (??.) which 

 partly enclose the oesophagus, and at a later stage do so wholly 

 (Plate IV. Fig. 36, n'.) The cells of these horns are found dividing in 

 unusual abundance. The horns lie next to the digestive epithelium, 

 and between it and the mesodermal lining of the ring canal. From the 

 method of growth, and from the sharp line of separation between the 

 tips of the horns and the surrounding tissue, there can be little doubt 

 that the circumcesophageal nerve of Paludicella, like the lophophoric 

 nerves of Phylactolsemata, arises as an outgrowth of the brain. 



Serial sections show that the ganglion suddenly diminishes in size 

 immediately below the point at which the circumoral nerves arise, but 

 one can trace a layer of cells continuous with the brain downwards for 

 ten or fifteen micra farther, to near the cardiac valve. At this point 

 one can still see nuclei of a third layer lying between the digestive epi- 

 thelium of the valve and the mesoderm. It seems to me, therefore, 

 that this may be regarded as a gastric nerve, which seems to originate 

 by a single root and later to give rise to two nerves, one of which lies 

 on either side of the cardiac valve. 



