OBSERVATIONS ON FRESH-WATER POLYZOA. y< 



as well as in the erect position of polypides. this species comes nearer 

 the genus Lophopus. The oelatinons substance is formed Ly the 

 secretion of cells of the outer layer of the endocyst. Numerous cells, 

 some oval, others irregidar in their shape, are scattered in it (fig. 6, 

 PI. XVIII.). Their nucleus and nucleolus are distinctly visible. 

 These cells seem to have wandered out of the outer layer of the 

 endocyst, and may have helped in producing the gelatinous substance, 

 remindin-T us of the cells in the test of the Tunicates. 'i'he gelatinous 

 substance is adhesive and without taste ; it ser\ es apparently to 

 protect the coh^ny. On drying, it shrinks almost to nothing. 



The endocyst consists of four layers (fig. 7, PI. XYIII.) 



a. Outer cell layer (OiU. Icuj.). 



h. Basement membrane (^Bas. vianhr.). 



c. Muscular layer (L. mus. and Tr. nuis.) 



d. Inner lining epithelium (Lin. cpith.). 



All of these layers are not present everywhere, nor is each ol 

 them of the same structure throuHiout its distribution. 



The cells of the outer layer, which represents the ectoderm, are 

 everywhere distinctly bounded, columnar on the cœnœcium, tiat and 

 h<)riz(jntally elongated on the polypide, except on the tentach^s and 

 the upper surface of the lophophore. In the former, they are culjical, 

 in the latter hexagonally prismatic, and distinctly ciliated in either 

 case. Many of the cells on the cœnœcium contain a vacuole (fig. 7, 

 vac.) filled with a very refractile fiuid. The numi)er of these 

 vacuolated cells increases as we ap[)roach the tip of cœnœcial branches, 

 where every cell shows a large vacuole, almost filling up the whole 

 cell (fig. 33, PI. XIX. Out. huj.). 



In preserved specimens, the cells are more or less shrunk, often 

 leaving' spaces between them. The nuclei are oval, and have a dis- 

 tinct, well-staining nucleolus. The cells on the cœnœciiun are 



