DR. WEBB, ON THE NOCTILUCA MILIARIS. 105 



trough or shallow concave cell is most convenient for obser- 

 vations on this part, as the animal swims close to the under 

 surface of the thin glass, and may be made to turn in any 

 direction. 



The ridge and tooth can scarcely be overlooked. This 

 ridge is of fibrous structure, and may sometimes be observed 

 in regular contractile action. Corresponding with these con- 

 tractions, I have witnessed a to-and-fro motion of the tooth, 

 as though working on an axis, in a direction towards the base 

 of the tentacle. A good illustration of this performance is 

 given by bending the fore and middle fingers and flexing 

 them on the palm of the hand. The tooth when seen in profile 

 has the appearance of a conical papilla (Plate VI., fig. 6), 

 or with a slight change in the point of view, of a hooked 

 process terminating in a sharp nib (figs. 8, 9). It readily 

 yields to pressure, and I have seen it become shrivelled up 

 from the use of astringents, before motion ceased in the cilium 

 and tentacle. 



The " vacuoles" are alimentary sacs. AVhen empty, they 

 are usually contracted and grouped near the membranous tube 

 which leads from the oral aperture, a few only being scattered 

 among the internal reticulations. Their situation is constantly 

 changing, sometimes with a steady advance, at others l)y jerks ; 

 while the fibrous meshes with which thev are connected 

 undergo a relative alteration in shape. Gentle pressure will 

 occasionally expel them through the oral or anal aperture ; 

 but I have seen them spontaneously ejected without rupture, 

 and float away from the body. In one instance where this 

 occurred, and where the contents consisted of granular matter, 

 fragments of Diatomacese, and particles of sand, the sac re- 

 mained entire for some time. When it buist, the membrane 

 doubled up, the contents escaped, and the bits of silica were 

 characteristically shown with the polariscope. I have never 

 known these gastric pouches, or alimentary substances to be 

 voided by any other outlet than those connected with the 

 central depression. 



The position of the second aperture, or arms, communica- 

 ting with the gastric pouch, appears to me to be at the pos- 

 terior end of this depression, on the side opposite to the 

 tooth, and somewhat further back (fig. 7). 



The mode of reproduction is at present far from being 

 satisfactorily made out. I have never met with a double in- 

 dividual, but on one occasion witnessed the process of division, 

 without, however, noting any proof of its connection with 

 that of fissipaious multiplication. Contractions of the in- 

 tegument took place in such a way as to cut off a globular 



