INTRODUCTION. 7 



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."* 



THE NUCLEUS. 



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 

 Haeckel (e. g. Biomi/xa 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."f 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 Ehizopoda 

 vary in point of number. This is not always uniform 

 in members of the same genus. Usually a single nucleus 

 is present, varying in size and well defined ; in certain 

 of the Lobosa and in some Heliozoa there are two or 

 more ; in Pelomi/xa 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. t Op. cit., p. 86. 



