64.0 C. H. MARTIN. 
it can attain a length of over 352 4. In the contracted condi- 
tion the outer wall of the proboscis is thrown into a series of 
wrinkled folds, and as arule only the tentacles at the anterior 
end are visible; but when the proboscis is fully expanded 
these folds disappear, and the proboscis then is seen as a long 
ribbon-shaped structure with a row of tentacles on either side 
down the greater part of its length. 
As arule even in the expanded proboscis only the apical 
tentacles are fully expanded, but a series of short knobs can 
be seen down the rest of the proboscis with the exception of 
a short basal portion indicating the positions of the retracted 
proximal tentacles (PI. 15, figs. 1 and 2). As the proboscis 
moves backwards and forwards, the apical tentacles move 
also, actively to and fro, so that the anterior end of a con- 
tracting or expanding proboscis looks rather like a portion of 
an active centipede. 
In sections of the proboscis each tentacle is found to pass 
as a continuous tube down the whole length of the proboscis 
(text-fig. la). Near the origin of the proboscis a large 
number of bands, which stain very lightly in eosin, arise. A 
single band passes up each tentacle tube in the proboscis, 
and is probably instrumental in the shortening of the tentacles 
and the proboscis (text-fig. 1b). These bands seem analogous 
to the myonemes of the stalk of a Vorticellid, and similar 
structures can be found in sections of the tentacles of other 
acinetaria, e.g. Ephelota. 
The investigation of the nuclei is rendered very difficult in 
fully grown forms by the presence of numerous masses of 
chromatin, the so-called Tinctin-kérper in the cytoplasm. 
The origin of these masses from the nuclei of the cells ingested 
during the process of feeding will be dealt with in a later 
section. In a young proboscidiform individual the macro- 
nucleus is a rod-shaped structure lying parallel to the animal’s 
long axis, in the later stages of growth it generally becomes 
more or less T-shaped, the two branches passing up into the 
apical lobes. 
In the young individuals a single micronucleus can always 
