THE MECHANISM OF LIFE 



517 



haviour of the nuclei observed by R. Hertwig ('88-'89) in the con- 

 jugation of ciliate Infusoria : l the fairly large macronucleus breaks 

 up into numerous separate particles and becomes completely re- 



FIG. 256. Form of the nucleus in secreting-cells. 7, Double cells with two nuclei from the egg- 

 follicles of Nepa cinerea. Between the two nuclei a mass of chitin is being secreted for the 

 formation of an egg-ray ; the nuclei have extended pseudopodia toward this side, so that the 

 secreted (granular) mass is circularly enclosed by the nuclear pseudopodia. II, Secreting-cells 

 from the spinning-glands of caterpillars. (After Korschelt.) 



.sorbed ; the micronucleus grows by the ingestion of substance, 

 differentiates, divides, and gives rise to a new micronucleus and a 



FIG. 257. Cells of salivary glands. A, At rest. The nuclei are star-shaped. B, After stimulation 

 of the gland. The nuclei are round. (After Heidenhain.) 



new macronucleus, which undergo a very considerable increase in 

 .size. 



It is unnecessary to extend still farther the enumeration of facts. 



1 Cf. p. 201. 



