NUCLEOLAR STRUCTURES OF THE CELL. 1 75 



cleoli in Carpocapsa and Eiichistns, these nucleolar structures 

 might be considered organs of the cell, e.g., centres of nutri- 

 tion, and so be of a nature essentially different from that of 

 the true nucleoli. 



In conclusion, the hope may be expressed that the study of 

 nucleolar structures will receive more attention in the future 

 than it has in the past. Whoever has had the patience to read 

 this brief summary of observations will grant that the nucleoli 

 are structures of manifold complexity, the study of the genesis 

 and fate of which may throw needed light upon questions of 

 cellular metabolism ; and there are three groups of animals 

 which bid fair to offer the best opportunity for work : the Pjv- 

 tozoa, and particularly the Mastigopkora and Foraniiiiifera, the 

 study of which must eventually give the best basis for cyto- 

 logical conclusions ; the Art/iropoda, which surpass all other 

 forms in the diversity of cellular structure ; and the Mollusca, 

 which in this regard are close rivals of the arthropods. 



