CYTOPLASM AND ACTIVATION OF THE GENE 267 



between genie action and cytoplasmic component are of this 

 type. It has to be added that the situation might be obscured 

 if genie action had produced the pattern of stratification already 

 before fertilization. In this case, only the maternal genes would 

 have taken part in the process, which thus may appear as an 

 independent cytoplasmic action. This situation was discussed 

 on page 206. 



3. CYTOPLASMIC HEREDITY 



The third problem is the one usually meant when the role of the 

 cytoplasm in heredity is discussed. Is the protoplasm not only 

 the substratum for the action of the genes but also an independent 

 part of the germ plasm, directly influencing the hereditary traits 

 by action of its own? 



A. Merogony 



It is known that some of the classic work in experimental 

 embryology was directed to a solution of this problem (Boveri, 

 Godlevski). In the experiments on merogony (purely paternal 

 nucleus in the cytoplasm of another species), first a positive 

 result was obtained, but this was later discarded by Boveri 

 himself as due to misinterpretation. In recent years, these 

 experiments have been revived with partly different methods. 

 Using the same method as Boveri, Hoerstadius (1936) produced 

 hybrid merogons between two species of sea urchins which could 

 be raised to the pluteus stage. The skeleton turned out to be 

 not typical. The club-shaped ends of the main calcareous rods 

 characteristic for one of the species (Psammechinus) are deter- 

 mined by the nucleus. They are intermediate in the hybrid and 

 typical in merogons with Ps. nucleus. In merogons with Ps. 

 plasma, abnormal rods appear; Hoerstadius, however, seems to 

 believe that this does not mean a plasmatic determination but 

 only an abnormality produced by the nuclear action in foreign 

 cytoplasm. 



The second method applied to such studies is the production 

 of germinal layer chimeras (von Ubisch, 1936; Hoerstadius, 1936) 

 in echinoderms by transplanting the micromeres of one species 

 into the blastula of another. In these cases, combination 

 skeletons may be formed which look very much like a hybrid 



