ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 389 



their Golden Age, and formed great deposits ; with the passing of the 

 Eocene period the Foraminifera lose their all-important position as 

 rock-builders ; nowadays a few pelagic genera are building up great 

 quantities of Globigerina ooze on the sea-floor. 



Selective Nutrition in Infusorians.* — S. Metalnikow finds that 

 Infusorians " learn " not to feed on injurious substances. They begin 

 by sweeping them in, but in several hours or days they cease doing so. 

 The less nutritive the substance, the quicker they are to cease ingesting 

 it. Thus they stopped ingesting emulsion of aluminium, sudan, red 

 phosphorus, and the like, long before they ceased ingesting carmin or 

 sepia particles. Of course, they may be killed right away by the first 

 ingesting, e.g. by particles of arsenic salt ; but if the substance experi- 

 mented with be not very injurious, they " learn " not to take any more 

 of it. 



In another paper t the author reports the results of further experi- 

 ments. He gave the Infusorians a mixture of carmin and sepia, to 

 others carmin alone, to others sepia alone. The majority did not ingest 

 the mixture, nor the carmin particles, but did ingest the sepia in large 

 quantities. Bacteria were ingested abundantly, so were aluminium 

 particles. But when carmin was added to the bacteria or to the aluminium 

 there was no ingestion. If sepia was added the ingestion went on as 

 usual . 



Effect of Conjugation in Paramoecium.J — H. S. Jennings has made 

 a large number of careful experiments bearing on this problem. The 

 chief positive results are : — (1) that conjugation increases -variation, 

 giving rise to heritable differentiations ; (2) that it results in bi-parental 

 inheritance ; (3) that the fission rate is lower after conjugation ; and 

 (4) that the mortality is as a rule higher, and abnormalities are more 

 common, among the descendants of conjugants than among those of non- 

 con jugants. 



In higher animals, fertilization initiates development and secures 

 bi-parental inheritance(which implies variety) — two logically independent 

 functions. In Infusorians conjugation has the role of securing bi-parental 

 inheritance, with varying mixtures of the characteristics of the two 

 parents. It is usually induced by an unfavourable change of conditions, 

 a change of such a nature that the organisms begin to decline. Then 

 conjugation occurs, so that new combinations are produced, adapted to 

 varied conditions, and some of these new combinations may survive. 



Conjugation does not produce rejuvenescence, for after conjugation 

 most of the animals are less vigorous than before. What conjugation 

 does is to bring about new combinations of germ-plasm. One result of 

 this is to produce bi-parental inheritance ; another is to give origin to 

 many variations, in the sense of inherited differentiations between dif- 

 ferent strains. Some of the new combinations are better adapted to the 

 existing conditions than others. 



* G.R. Soc. Biol. Paris, Ixxiv. (1913) pp. 701-3. 

 t G.R. Soc. Biol. Paris, Ixxiv. (1913) pp. 704-5. 

 X Journ. Exper. Zool, xiv. (1913) pp. 279-391 (2 figs.). 



Aug. 20th, 1913 2 D 



