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- 
