INFUSORIA PARASITIC IN CEPHALOPODA. 195 
the youngest animals, the nucleus is roughly horse-shoe 
shaped, but in large individuals it takes the form of a mesh- 
work of chromatin containing nucleoli at certain points. 
The network, which varies in its form, is described as con- 
sisting of a system of “tubes,” and as being ‘‘ amceboid.” 
It bears, as Caullery and Mesnil have pointed out, a very 
striking resemblance to the nuclear apparatus, as | have seen 
it, in Opalinopsis. 
But the most interesting comparisons are to be made with 
various Anoplophryine. Recent research has brought to 
light many interesting facts regarding this group. As is 
well known, in Anoplophrya the nucleus is band-like, run- 
ning down the middle of the body of the elongate organism. 
The animals possess a series of vacuoles and a method of 
segmentation which resemble the conditions seen in Chro- 
midina to a remarkable degree. But at first sight the 
nucleus appears totally unlike. The means of comparison 
have been given us by Caullery and Mesnil (4), who have 
discovered a remarkable new member of the group—Khizo- 
karyum concavum,C. et M. In this animal—a parasite of 
certain species of Poly dora—there is a nucleus consisting of 
a thick axis, from which numerous branching processes are 
given off (“like a root with numerous rootlets”). According 
to these observers, in Anoplophrya also the central nuclear 
cylinder sometimes shows little pointed appendages, thus 
presenting an appearance intermediate between a simple 
band and a branching stem like that of Rhizokaryum. 
From the latter condition it is not difficult to imagine how a 
reticular nucleus like that of Chromidina might have 
arisen from an originally compact nucleus. The last barrier 
between the infusorian parasites of cuttlefish and the Ano- 
plophryinz has now been broken. And it is certain, as 
Neresheimer (13) hinted from his study of Opalina, that 
the parasites from cephalopods are not related to 
Opalina but to Anoplophrya. 
One or two other points of interest may be briefly touched 
upon. ‘The most interesting is the apparent absence of a 
