ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
157 
wliicli has certainly been seen by many observers. There is no doubt 
that in karyokinesis the nnclens has an essential influence on the cell. 
There is an indistinct boundary in most of the branched nuclei of 
the nutrient cells of the ovaries of Insects, and often also in those of the 
spinning-glands of caterpillars ; here, too, we may conclude that the 
nucleus exercises a direct influence on tlie cell. In secreting cells 
the indistinctness of the nuclear boundary is often manifest. In the 
nutrient cells of Insects’ ovaries, in the spinning-glands of the larvee of 
Lepidoptera, Neuroptera, and certain Hymeno2)tera the nuclei, without 
distinct boundaries, extend through the whole cell, send out processes, 
and ramify. In this way they are brought into close contact with all 
jmrts of the cell, and can thus best exercise their influence. 
We cannot doubt that the nucleus takes uj) and gives off substance 
when we see how the nucleus increases and diminishes in size ; this can 
be best followed out in the ovarian cells of Dytiscus marginalis. A 
change in the structure of the nucleus is connected with the share it 
takes in the activity of the cell ; those changes find expression in the 
heaping uj) of masses of chromatic substance which disappear again 
later on. Nuclear bodies may be present in or absent from the nuclei, 
and in the former case, they may vary both in number and form. The 
germinal spots have, notably, had especial significance ascribed to them. 
In the young ovarian nuclei of Insects, and in the nuclei of the secreting 
double cells of the ovaries of Nepa and Hanatra there are large bodies 
which, later on, partly disaj^pear. The nuclei of the spinning glands 
have very different structures at different times ; the plexus has various 
phases of closeness, and by the disaj^pt arance of the network the nuclei 
get to have an empty appearance, and have a large quantity of achromatic 
substance in their interior. The nuclei of the spinning gland of Cladius 
difformis present other characters; the nuclei of the glandular cells are 
at first spherical, but later on they branch, and at last appear only as 
thin filaments of homogeneous structure which stain deeply. 
The author discusses the views of previous writers on the function 
of the nucleus, and comes to the conclusion that the separation of the 
nucleus from the cell-protoplasm is only apparent. In reality there are 
close connections between them ; where there is a nuclear membrane, 
there may be diffusion, or there may be spaces in the membrane by 
which the two may communicate, or there may be no membrane when 
the network of the nucleus passes directly into that of the cell- 
j)iotoplasm. At different times the nucleus has different relations to 
the plasma, and these are sometimes closer than at others ; there is no 
doubt that this is connected with the functions of the cell in which the 
nucleus takes part. But the removal of the boundar}' does not always 
seem to be sufficient, for in some cases the nucleus changes its position, 
and makes its way to the part of the cell which is in the greatest 
activity. The change in form may be temporary or permanent. The 
influence of the nucleus does not appear to be requisite for all the 
manifestations of the activity of the cell— for example, the non-nucleated 
parts of Algar cells were found to be capable of assimilation, but they 
were, on the other hand, unable to form a new cell-membrane. Non- 
nucleated particles of Infusoria are incapable of replacing lost parts, 
while nucleated pieces do so easily. 
