190 CORA J. BECKWITH 



A. Hydractinia 221 



1. Nucleus of the growth period 221 



2. Maturation 222 



3. Fertilization 225 



4. Fertilization-membrane and mitochondria 225 



5. Nucleolus 226 



6. Chromosomes and continuity 228 



B. Eudendrium 228 



1. Maturation 228 



2. Fertilization 228 



V. Summary 230 



Bibliography 232 



I. INTRODUCTION 



This paper is offered as a contribution to the discussion con- 

 cerning the origin and relationship of the protoplasmic^ granules, 

 especially the chromidia and mitochondria. Although this 

 complex and difficult problem has received much attention, it is 

 still far from a satisfactory solution. A considerable group of 

 observers, including Goldschmidt and his followers, have endeav- 

 ored to extend Richard Hertwig's conception of chromidia in 

 Protozoa, to certain of the protoplasmic granules in the metazoan 

 cell, attributing a nuclear origin to the latter (chromidia) and 

 regarding them as only temporary elements of the protoplasm. 

 A second group of observers, led especially by Meves and Dues- 

 berg, are highly skeptical in regard to this hypothesis and have 

 reached the conclusion that the most constant and characteristic 

 of the granules (mitochondria, plastochondria) are purely proto- 

 plasmic in origin. According to them, the granules in question 

 form an essential constituent of the protoplasm and are permanent 

 cell-elements which exhibit a genetic continuity, and are the bear- 

 ers of protoplasmic heredity ('plastochondrial germ-plasm') . The 

 present paper is concerned especially with the conclusions of 

 Schaxel, which are more or less intermediate between the two 

 foregoing conceptions. He finds both types of protoplasmic 

 granules present, 'extra-nuclear chromatin-granules' (corres- 

 ponding to chromidia) which control differentiation, and mito- 

 chondria of purely protoplasmic origin. 



* The term 'protoplasm' is used throughout the paper instead of 'cytoplasm', 

 according to the usage of the earlier writers on the subject. 



