HYDRACTINIA. 



21 



extend for some distance beyond the edge of the shell, and 

 to form a considerable addition to the lip. This portion 

 can be readily removed and submitted to the microscope. 

 A careful examination of this free extension of the crust 

 has yielded the following results : The upper surface is 

 invested by a white fleshy substance, from which the poly- 

 pites and spiral organs are developed in large numbers, 

 the latter almost exclusively on the extreme margin. On 

 examination, this soft layer is found to be mainly com- 

 posed of a multitude of delicate, anastomosing, tubular 

 stolons closely packed together. The surface of the layer 

 is more or less roughened by minute points of chitine, 

 which protrude through it, and, running in lines, mark 

 out the course of the stolouic tubes. At intervals large 

 grooved and muricated spines occur, which are also partially 

 covered by the fleshy crust. 



If a portion of the base be divided transversely so that 

 the intimate structure may be examined in section, the 

 following appearances are observable. 



Fig. 1. 



A large proportion of the slice is seen to be occupied by 

 a chitinous framework (fig. I, a a), the upper side of 

 which is overspread by the fleshy carpet that bears the 

 polypites (fig. 1, b b}, while the inferior surface is more or 

 less covered by a thin layer of a mucus-like substance 



