492 AUSTRALIAN FRESHWATER POLYZOA, I., 



extension it is of an hourglass-shape; when partly extended it is- 

 an attenuated cylindrical tube; well withdrawn, it passes from a 

 swollen cylindrical form into that of a cone, whose haae is at tlm 

 oral extremity, according as the retraction is partial or complete. 

 It passes into the stomach, into which it is continued as a valve- 

 like structure, which, although plainly visible in the perfectly 

 extended polypide, is best shown under a certain amount of 

 retraction. In transverse section it is circular, measuring, in the 

 region between the mouth and anus, about 0'55 mm. in diameter^ 

 and in this protrusible portion of the polypide, constitutes the 

 greater part of a section. It is lined by a layer of columnar 

 cells with centrally situated nuclei, the height being about 2^-3- 

 times the breadth. The cells are provided with long flagella irt 

 the part of the oesophagus lying between the mouth and the anus. 

 Below this region no flagella are visible. Nearing the region of 

 the stomach, the cells are much more compactly arranged, to pass 

 into the lining layer of the stomach, and the nuclei are situated 

 at the outer extremity of the cells. The oesophagus in this 

 region has become more elliptical in shape. 



The stomach and intestine are shown in figs. 2-4, in conditions 

 of retraction and extension. The stomach is lined by cells, vary- 

 ing in shape in different regions, and with basally situated nuclei. 

 At the oral end of the stomach, the lining cells are columnar; in 

 the aboral region, the cells are clavate and columnar, and the^ 

 wall has a sinuous contour. The cells lining the intestine are 

 not so compactly arranged as in the stomach, and are cubical. 



Nervous system. — A nerve-ganglion is present in close contact 

 with the oesophagus on its anal side. It has a flattened reniform 

 shape, and is inconspicuous in entire mounts. The cells composing; 

 it have a loose arrangement. 



JxeprudiLctive organs. — No definite sexual organs were visible- 

 in the specimens examined. 



StcUoNasts. — Occurring in the same tube, one finds statoblasts 

 quite difterent in shape and measurements. For instance, I have 

 noted, in the same tube, statoblasts of which some are of a 

 perfectly broad elliptical contour, some shading from this into aa 



