686 MURIEL ROBERTSON. 
regarded as a true nuclear membrane in the metazoan sense, 
and I do not wish the word to be taken as implying homology. 
I have never been able to see on hematoxylin preparations 
any strands passing from the karyosome to the membrane, 
although it is a very usual feature in this type of nucleus. 
It is to be noted that the protoplasm shows no differentia- 
tion round the membrane of the nucleus, that is to say, that 
in the wet method films stained with hematoxylin there is no 
protoplasmic halo. 
A slightly different appearance is presented in the dried 
films here (Pl. 16, figs. 3 and 4), there is a wide protoplasmic 
halo which always takes the blue stain of the Romanowsky 
combination much less deeply than the surrounding cell 
substance. 
Approximately in the centre of this is the karyosome, which 
is composed of a blue staining substance underlying a reticulum 
of red staining chromatin. In some specimens strands seem 
to pass out from the karyosome—occasionally a pale (fig. 3) 
red ring surrounds the karyosome and strands may be seen 
passing between them. It is to be noted that this ring is 
well within the protoplasmic halo. My interpretation of the 
Romanowsky appearance is as follows :—The red ring corre- 
sponds to the membrane (in the Heidenhain preparations) 
which is generally destroyed in the drying. 
What I have called the protoplasmic halo in the Roman- 
owsky picture corresponds to the space between the karyo- 
some and the membrane, but it is much widened by the pulling 
back of the protoplasm due to the general flattening of the 
whole organism. 
As before noted small specimens are present, the origin of 
these (Pl. 16, figs. 5 and 6) is still obscure; they may either 
arise from the large forms by division or they may possibly 
be the young forms derived by infection from the leech. I 
am inclined to consider the former explanation as the more 
probable. It is, however, impossible, to form any very 
reasonable opinion on the point except from the results of 
experimental inoculation. 
