INTRODUCTION. 7s 
The conclusions of the authors cited represent, 
broadly speaking, the present state of our knowledge 
upon this subject. It may be said to accord with 
general observation that, so far as there is a regional 
difference in the plasma-body between endoplasm and 
ectoplasm, it possesses no morphological significance, 
but is, as Calkins observes, “ only an index of the 
physical conditions of the protoplasm.”* 
Tue Nucteus. 
The nucleus plays an important part in the develop- 
ment and functions of the protoplasmic cell. There 
are certain organisms belonging to the Monera of 
Heckel (e.g. Biomyxa vagans) in which no nucleus has 
yet been satisfactorily demonstrated. It does not 
follow, however, that nuclear substance is absent, for, 
as Calkins says, nuclei are “almost as varied in the 
different forms of Sarcodina as are the different types 
of the animals as a whole.”t+ In some cases where a 
nucleus is present, it is ill-defined, the chromatin, a 
part of the nuclear substance stainable with certain 
basic dyes, being scattered in the form of granules 
throughout the entire cell. It is possible, this author 
further says, to conceive of non-nucleated organisms, 
although the numerous experiments on nucleated and 
non-nucleated parts of Protozoa show, in these cases at 
least, the absolute necessity of the nucleus for the life 
of the individual. 
The nuclei observed in different species of Rhizopoda 
vary in point of number. This is not always uniform 
in members of the same genus. Usually asingle nucleus 
is present, varying in size and well defined; in certain 
of the Lobosa and in some Heliozoa there are two or 
more; in Pelomyxa palustris, nuclear bodies, it is 
asserted, can be counted by the thousand. The 
testaceous genera (Arcella, etc.) are in many cases 
multinucleated. There may, in some forms, be a mem- 
* ©The Protozoa,’ p. 38. + Op. cit., p. 86. 
