PROCEEDINGS OF SOCIETIES. 41 



of fixed structures at the sea-side. The fresh-water polyzoa, which 

 you will encounter readily about here, will be perhajjs those most 

 familiar to you, and so I propose to introduce one of these fresh-water 

 kinds as a type of the rest. All this great fungus-looking mass is 

 composed of a number of animals congregated together ; this was 

 captured in Mr. Thrale's lake on Tooting Common. If now you look 

 at the hard structure, you will see that it jiresents at all jjoints little 

 cavities, which are the oiDeniugs of long tubular cells into which the 

 softer substances are retracted. These cells are lined by delicate 

 animal matter ; and this matter projects beyond the mouth of the cells 

 in the form of a soft tube of a somewhat conical shape. The cone, at 

 its termination, suddenly exj^ands into a structure called the lopho- 

 phore, or plume-bearing structiu-e. In most of the familiar forms, this 

 is in the shape of a horse-shoe placed flat, and along the sides of this 

 horse-shoe run two series of tentacles parallel to one another. These 

 expand into a beautiful crown, which may be compared to the body of 

 one of the old-fashioned chariots. On the disk where the lophophore 

 is attached, we find the commencement of the alimentary canal — the 

 mouth — enclosed by the arms of the lophophore, and lying between 

 the double row of the tentacles. On viewing the living animal you 

 will see that these tentacles by means of their cilia cause little whirl- 

 ing currents, so arranged as to bring solid matters suspended in the 

 water down into the hollow cup, and thence into the mouth ; from the 

 mouth they go to the pharynx, which is richly fringed with cilia, and 

 thence to the stomach. In the walls of the stomach we find usually a 

 number of little cells, containing dark-brown matter, which are sup- 

 posed to discharge the function of a liver. Surrounding the alimen- 

 tary canal is a cavity called the perivisceral cavity. This contains a 

 fluid, which is all the creature has to represent blood ; this fluid cir- 

 culates in all parts of the body. As to their respiration, they draw 

 oxygen from the water around them ; this is done in part by their 

 tentacles, also by drawing in water, with regular alternating actions of 

 suction and ejection. With regard to the organs of reproduction, one 

 may note that these creatures reproduce themselves in at least three 

 ways. First, by eggs, the result of the impregnation of ova with sper- 

 matozoa ; the ova undergo their development within the body, as far as 

 can be made out. The embryo is first a hollow sphere ; a layer is 

 then thrown off from the surface at the same time that an ojDening 

 is made in the wall of the sphere ; a second sort of little sphere is thus 

 formed within the first, and here little polypides are gradually de- 

 veloped. A second way of reproduction is that on the side wall at 

 some point or other a projection occurs, and grows to a tube in which 

 all the parts of a new polyinde are by degrees developed ; and by a 

 third form of development, we find towards the latter part of the autumn 

 dark, flat, oval bodies forming themselves. They are comj^osed of two 

 slightly convex plates like watch-glasses placed face to face, wdth ger- 

 minal matter inside. These eggs live through the winter from the 

 autumn, nearly all the composite structures dying as winter comes on. 

 These bodies receive the name of statdblasts, from the idea that they 

 remain in the dead organism silently awaiting the spring. Their forms 



