83 



shall fall within, and that hanging from the zigzaged circle 

 shall fall on the outside. Over both wires draw, smoothly, a 

 separate cloth, to which fix both wires. Then, by holding 

 the entire contrivance at any point of the plain wire circle, 

 the whole will be retained in its place. Such a contrivance will 

 afford the best idea of the very remarkable arrangement of the 

 internal membrane of the present species, and of the object and 

 importance of its deeply extended head. It is obvious that, if 

 the lower wire were zigzaged, not only in its horizontal plane but 

 also in a direction perpendicular to that plane, though it would 

 affect the points at which the outer covering or envelope would 

 be touched, it would in no wise affect the principle of the plaits 

 or folds whose extremities touched that envelope. The following 

 two figures may render this matter still clearer. 



In each figure the dotted line is the envelope. Fig. H is a 

 longitudinal section as it would be seen if one could be taken 

 exactly clear through any spot where there was no lateral divi- 

 sion of a plait the presence of which gives a false appearance of 

 anastomosis to a section. It will be seen that the membrane 

 may be traced from the point of the base to c and thence to a 

 in a continuous line, and that the projecting plaits are affixed, at 

 various points, to the envelope a b. Fig. I is a transverse sec- 

 tion taken about the middle of a specimen. The inner circle is 

 the membrane where simple and unwaving, and forming there- 

 fore necessarily an unbroken circle. Between this and the en- 

 velope the plaits are seen, cut horizontally across. 



The membrane begins to fold upwards in its last plait at dif- 

 ferent distances in different specimens from the inner margin of 

 the head ; and it is rarely that the folding upwards will take place 

 on exactly the same plane all around ; whence, on section, a de- 

 ceptive appearance is often given, as if there were a double or 

 triple or still more numerous ramification of the central cavity. 



F2 



