SOME OBSERVATIONS ON ACINETARIA. 361 
(1888); he separated it from Acineta tuberosa, which 
it somewhat closely resembles owing to the presence of 
characteristic “valves”? near the junction of the theca with 
the stalk, and to the fact that the body of the animal is 
usually not attached to the base of the theca. Keppen 
found it in both fresh and salt water in the neighbourhood of 
Odessa. 
I first found this acinetarian in June, 1907, growing in 
great abundance on the hydrocaulus of Cordylophora 
lacustris, in Hickling Broad, the water of which is shghtly 
brackish. It seemed to be feeding mainly on Stentor, 
which was at this time very abundant in the broad. As 
regards the main features of its structure, I have nothing 
material to add to Keppen’s account, except as regards the 
relation of the theca to the body of the Acineta, and also as 
regards some details in the process of reproduction. 
The “valves.’’—I always found three of these structures 
at the junction of the theca and the stalk, presenting under 
a low power an appearance corresponding with Keppen’s 
figures, but in the interpretation of this appearance I should 
feel inclined to differ from Keppen. 
Keppen regards these structures as three parallel plates 
cutting off the cavity of the stalk from that of the theca. I 
think that this appearance is merely the optical expression of 
a joint consisting of a short tube overlapping the ends of the 
stalk and of the theca. 
These structures are unfortunately very difficult to make 
out in permanent preparations, but I arrived at this inter- 
pretation from an examination of the living animal before I 
had seen Keppen’s paper, and it is, I think, confirmed by 
longitudinal sections (cf. text-figure 1). This interpretation 
would explain the frequent occurrence of individuals which 
have bent laterally at the junction of the stalk and the 
theca, so that the apical surface faces the base of the stalk. 
‘his bending is in some cases, I believe, purely passive, but 
I have often seen animals turn in this way by wrapping 
their tentacles around the stalk, and so pulling themselves 
