84 EVENINGS AT THE MICROSCOPE 



Besides the hind bands, there is one, or a pair of simi- 

 lar muscular bands, attached on each side of the front part 

 of the base of the cell, and inserted similarly into the 

 neck. By watching the contraction of these, you will be 

 enabled to determine the use of the membrane- covered 

 aperture up the front of the cell. At the moment of the 

 retraction of the viscera into the cell, a large angular mem- 

 brane is forced outward from the front side, which is pro- 

 truded more or less in proportion to the degree of with- 

 drawal of the polypide; and as the latter emerges again, 

 the membrane falls back to its place. It is evident, then, 

 that this is a provision for enlarging the cavity; the walls 

 are horny, and probably almost inelastic; but when the 

 stomach forces the intestine forward, and the thick gullet 

 is bent outward by the withdrawal of the neck and ten- 

 tacles, the needful room is provided by the bulging out 

 of this elastic membrane, which recovers its place by the 

 pressure of the surrounding water, when the pressure of 

 the fluids within is removed. 



Now, after watching these movements of the polypides, 

 and the various structures whose forms and limits those 

 movements reveal, it will become manifest to you that 

 there is no visible organic connection between the animal 

 distinctively so called and the curious bird's head. This 

 latter has a muscular system of its own, by means of which 

 its energetic motions are performed; but it appears quite 

 isolated on the outside of the calcareous cell, and wholly 

 cut off from the interior by the knob on which it works, 

 and by the thickness of the cell- wall. Both knob and wall 

 appear quite imperf orate; and yet we cannot but presume 

 that some connection exists, perhaps through the medium 

 of an excessively delicate and subtile, but living tissue, 



