264 lULFJiTrX 120, UNITED STATES NATIONAL MUSEUM. 



it is about eiiiially tliit-k over tlie whole body. Similarly in some 

 species, \mt not in others, the endosarc is more dense anteriorly and 

 has the endospherules more numerous in this region. 



The general appearance of the cytoplasm and its alveolation dif- 

 fers in different species, but this prol)ably differs also with the 

 physiological condition. This character intiuences the observer, per- 

 haps unconsciously, but it should be used with caution. 



Tlie size and the shape of the endospherules seems a rather con- 

 stant specihc character, though in a few species they are quite diverse , 

 in size and somewhat so in form. The endospherules are not well i 

 shown with most stains. Iron hematoxylin rightly nsed brings them 

 out ver}' clearly. 



The position of the nuclei is a helpful diagnostic character in some 

 species of ProfoopaHna and ZellerieUa. In some species of Opa- 

 linlnde the nuclei are more close together in the front end of the 

 body, or at one edge of the front of the body in some Opalinas, while 

 in other species the nuclei are evenly distriliuted throughout the body. 

 The size of the 7iuclei is a most useful diagnostic character if only 

 one is sure that he is comparing individuals from the same phase 

 of tlie life cycle. It would not do to compare primary nuclei with 

 secondare" nuclei, if it should prove that there are these two sorts of 

 nuclei, as Neresheimer describes. If the numerous small nucleus- 

 like bodies are parasites {Sphaerella?}, they may lead the unwary 

 observer into no less serious error. There are also indications that 

 nuclear size varies with i^hysiological state, in the Opalinas at least. 

 For example, in O. ranarxun and its several formae^ nuclei whose 

 macrochromatin is in the form of small scattered granules tend to 

 be larger than nuclei whose macrochromatin shows certain large, 

 disklike aggregations beneath the nuclear membrane. Hegner and 

 Hsiang-Fong Wu (1921) shoAv that in Opalina \larvaru?n'] there is 

 decrease in size of the nuclei as the young OpaUnae grow larger. 

 Nuclear size, therefore, can not be used without scrutiny as a specific j 

 diagnostic character. 



Tlie shape of the resting miclei has been emphasized as a readily 

 discerned and apparently reliable specific character. In some of the 

 multinucleated species the dimensions and proportions of the divid- 

 ing nuclei, say, in the anaphase stage, are distinctive, some species 

 having rather broad ellipsoidal anaphase nuclei, other species very 

 slender spindle-shaped anaphase nuclei, and other species being inter- 

 mediate in this character. 



The mitotic condition of the nuclei we have also emphasized in 

 describing the species of Protoopalina and to a less extent the species 

 of ZellerieUa. The stage of nuclear mitosis at which the division 

 of the body occurs seems to be specifically constant within rather 

 narrow limits. 



