638 MUSCULAR TISSUES IN HYDROID POLYPS, 



Polypo-medusse and Syphonophorao. In an ordinary transverse- 

 section a radial structure of this muscle can be detected. By 

 means of very fine transverse sections we can obtain an insight 

 into the minute structure. 



From the structureless supporting lamella longitudinal sup- 

 porting ridges rise up on the sides of which muscular fibres are 

 situated. The free margins of these ridges are continued into the 

 centripedal ends of the epithelial cells, which form the Ectodermal 

 Epithelium. These are at the same time Chitin-gland cells ; near 

 the outer margin they appear slightly striped radially, and are 

 continued into the substance of the cuticle or the Perisarc, according 

 to whether the section has been made in a higher or a lower part. 



The section, fig. 1, lies in the same height as that in fig. 4 ; the 

 thin cuticule is cut. 



In adult animals these cells are not entirely filled with Proto- 

 plasm attached by a broad basal surface to the inner surface of 

 the Cuticle, these cells appear as pyramids with a radially situated 

 axis. Centripetally their width rapidly decreased, and they 

 continue without apparent limit into the margin of the supporting 

 ridges. The space between the basal ends of these cells and 

 between the opposite muscular lamella) is taken up by a granulose 

 mass in which nuclei can be made visible by coloring. A great 

 many of these nuclei probably belong to the sub-epithelial muscular 

 cells. Whether some of them belong to ganglia-cells appears 

 doubtful, but I consider it nevertheless highly probable. Part of 

 tli is mass probably also consists of nerve fibres. There are 

 accordingly longitudinal bonds of tissue which are vertical on the 

 surface of the Hydranth. Between every pair of muscular bands 

 lies a band, consisting of nervous fibres and ganglia cells. These 

 are enclosed on the outer side by ordinary epithelial-cells. 



