36 



space; to these are giveu tlie name of statoblasts. .From the 

 earliest period that the fresh-water polyzoa became an object of 

 studj', the statobhists attracted the attention of observers. 

 Their form is not exactly the same in the different species, they 

 vary accordingly from an orbicnlar to an elongated oval figure, 

 ami are enclosed in a horny shell, which consists of two concave 

 discs, united by their margins, where they are further strength- 

 ened by a ring which runs round the entire margin, and is a 

 different structure from the disc. The ring is composed of cells, 

 which are generally larger than the cells of the disc, and of a 

 different colour ; they are filled with air, giving the ring a light 

 spongy texture, and act as a float, by which the statoblasts when 

 free are kept near the surface of the surrounding water. When 

 the statoblasts are placed under favourable circumstances for 

 their development, they open by the separation from one another 

 of the two discs, or faces, and there then escapes from them a young 

 poh'zoon, already in an advanced stage of development, and in 

 all essential points resembling the adult individual in whose cell 

 the statoblasts were jn'oduced. At the period of its escape it 

 possesses all the essential organization of the adult ; the 

 retractor muscles are well developed and the polj'pied is capable 

 of regular exertion and retraction. Another way by which the 

 polyzoa is multiplied is by gemma, or budding, during the summer 

 months. The first appearance of the bud is seen near the 

 orifice of the cell, in the form of a minute spherical tubercle, 

 which gradually increases in size, and is thus pushed out through 

 the ectocyst, or external investment. At the same time the ali- 

 mentary canal begins to form, the three regions of which, 

 namely, the esophagus, stomach, and intestines are easily dis- 

 tinguishable, and the full development is soon completed. 



NOVEMBER. 



On the Sea Mouse fApJirodita AcuJcataJ hj Mr. S. Saunders. 



Aphrodita aculeata, commonly known as the sea-mouse, a 

 creature whose habitat is deep water with a muddy bottom. On 

 being brought up in the dredge the animal presents a strange 

 combination of dirt and beauty. The body is clothed with a 

 c|\iantity of sUky hair ; that which fringes the sides being long, 

 delicate, and of metallic lustre, reflecting the most beautiful 

 prismatic colours, but the liair with which the back is covered 

 retains on its surface a cj^uantitj- of mud and slime. This hair 

 is matted together, forming a substance like felt, which is quite 

 detaclied from the body of tlie animal, and can be lifted by 

 means of fifteen pairs of delicate plates, which shield the 

 breathing organs ranged in a double row upon the back. A 



