654 i THE AMERICAN NATURALIST. [Vor. XXXV. 
Actinobolus radians St. 
This infusorian is much more rare than Lacrymaria, and from 
its rarity perhaps more interesting. It was first described by 
Stein, then by Entz, who studied it very carefully, and later 
by Von Erlanger, who made out a number of minor points of 
structure. It is almost always found in the company of certain 
forms of Suctoria, Von Erlanger alone not finding these asso- 
ciates. In the Van Cortlandt water the organism was over- 
looked for some time, because of its supposed identity with the 
suctorian Sphzrophrya, which was present in considerable 
numbers. Actinobolus is a small spherical organism not much 
larger than a Urocentrum, 
ae and when at rest resem- 
‘Nal Wi) bles a Sphzrophrya, 
S NS NN i Hd Vy which in turn resembles 
: WSS Mg A an Actinophrys. It is 
only when this form is 
studied with a medium 
high power that a fringe 
of vibrating cilia can be 
* made out around the 
^ 7 i uem NÑ NN profile of the périu 
/ DN M a AN mA NN `N, It may then be seen that 
B M i il C there are groups of long 
| cilia (ten or twelve to a 
Fic. 3.~ Actinobolus radians St. The tentacles are group) arranged about - 
th side withthe small mouthinadvance, Themes the base of each of the 
is elongate and constricted. Six Halteria are faintly long tentacle-like proc- 
represented in the endoplasm. x 1200. 
esses, which give to the 
organism, when at rest, the aspect of a heliozoón (Fig. 3). 
The tentacles are the most interesting feature of the ciliate, 
and their function has been in considerable doubt. Stein was 
unable to assign any function, but described them as retractile, 
like the tentacles of the Suctoria, to which he compared them, 
observing at the same time that they might be entirely with- 
drawn into the body, leaving no trace of their former presence. 
Entz thought that they might assist the organism in getting 
