142 NATURAL HISTORY OF 



after being cut off, to coil and uncoil themselves whilst 

 under examination. The acontium is ciliated all over, 

 and is either kidney-shaped in transverse section 

 {Hertwig) or flat, but capable of bringing its edges 

 together so as to form a tube (Gosse). 



The acontia are often emitted through the body wall 

 of the column, which, in many species, is provided with 

 special loopholes for the purpose. These loopholes 

 were first discovered by Mr. Gosse, who gave to them 

 the name of cinclides. (See Plate XI. fig. 6.) They 

 occur in the Sagartidee, and are described by Mr. Gosse 

 as presenting an appearance such as would be presented 

 by the lids of the human eye, supposing them to be 

 reversed. The cinclides appear to be covered by a 

 thin membranous film, either of mucus or epithelium. 

 An interesting description of the cinclides and the 

 acontia is contained in Mr. Gosse^s " Hours with the 

 Microscope.''^ 



The thread cells with which the acontia are crowded 

 are remarkable structures. Three forms have been 

 observed and described by Mr. Gosse. 



1. Chambered cnidae, which are lengthened, egg- 

 shaped cells, containing a fusiform chamber opening 

 out at the broader end and continued at the other end 

 into a long cord or thread {the edlioreum), which fills 

 up the cell and is often many times longer than the 

 cnida. The ecthorea are generally armed with spiral 

 bands or screws [strehla], to which are attached barbs 

 or bristles {pterygia). (See Plate XI. fig. 5 h, c.) 



2. Tangled cnidse, in which the figure of the cnida 

 is almost oval. The cavity contains a very long edho- 

 reum, which is coiled up often in a loose and irregular 

 manner. 



