On Ophrydium versatile. 



47 



contract and expand in a very curious manner. The in- 

 fusoria themselves are separated from each other by a small 

 quantity of gelatinous matter, which, as it is secreted by 

 each individual, appears as if cellular. The free extremity, 

 where the mouth is situated, has a number of cilia placed 

 round it, while the mouth has a lid, ciliated round the edge, 

 which shuts down. The cilia form but a single band, which 

 is reflected from around the mouth, along the edge of the lid. 



If one of the gelatinous masses be placed in a watch-glass, 

 in a short time all the animals escape. The individual In- 

 fusoria are, when fully expanded, about the one-hundredth 

 of an inch in length. After the animals escape they acquire 

 a second band of cilia, which enables them to swim with 

 great freedom through the water. The individuals observed 

 generally escaped at the end of eight or ten days, leaving 

 nothing but a mass of jelly, which does not dissolve after two 

 months' standing in cold water. Sometimes no second band 

 of cilia appears, and then three furrows were seen running 

 along the whole length of the body in a spiral manner, 

 which gave a rotatory screwing motion to it, and enabled 

 the animal to move backwards rapidly. The cilia being the 

 propelling power, the animal moves with the aboral pole 

 forwards. Near the oral extremity is situated the transparent 

 vesicle or nucleus; this is quite visible when the animals are 

 attached, but shortly after they become free it disappears. 

 It breaks up into numerous small spherical vesicles, which 

 are called the yolk-masses by Dr Balbiani. The researches 

 of Dr Balbiani show that the contact of the oral extremity 

 of two hermaphrodite Infusoria is necessary for the disap- 

 pearance of the nucleus: this I have never seen in Ophrydium, 

 although it may occur. Dr Balbiani's observations tend to 

 show that the nucleus is the ovary, and the nucleolus the 

 testis. All the observations made on the Ophrydium show 

 that the nucleus produces the spherical bodies, or yolk- 

 masses, which are developed into the perfect animals. The 

 testis or nucleolus has not been observed in the Ophrydium, 

 but in all probability it does exist, although it may escape 

 detection without careful examination with a good micro- 

 scope. The nucleus, as has been said, breaks up and dis- 



