PEEFACE. 



THE preparation of a monograph dealing with minute organ- 

 isms, where the descriptions of the old authors are compara- 

 tively or often absolutely valueless, depends on the facilities 

 afforded for a critical examination of type or authentic speci- 

 mens. In this respect I have enjoyed exceptional facilities. 

 The splendid collection of Myxogastres in the Royal Herbarium, 

 Kew, rich in types, and with numerous annotations by Rosta- 

 finski, who examined the collection in detail, and which indeed 

 served as the basis for his excellent monograph, also served me 

 in like manner. To other workers in the same field in different 

 countries I am also indebted for the loan or gift of valuable, 

 and in some instances unique, specimens. To all who have in 

 this or other ways assisted, I offer my sincere thanks. 



Notwithstanding the excellent work initiated by the late 

 Professor De Bary, and continued by Brefeld, Cienkowski, 

 Woronin, Zopf, and others, the life-history of the majority of 

 forms is still unknown ; hence all attempts at classification, as 

 also the conception as to what constitutes a species, must be 

 considered as tentative. When we are better aquainted with 

 the main lines of development and lines of variation, also the 

 conditions determining these variations, it is certain that the 

 main factor in the discrimination of species will not be a one- 

 twelfth oil-immersion objective. 



GEO. MASSEE. 



Kew, 1892. 



