THE MECHANISM OF LIFE 



517 



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

 jugation of ciliate Inficsoria : ^ the fairly large macronucleus breaks 

 up into numerous separate particles and becomes completely re- 



FlG. 2rii). — Form of tho nucleus in secreting-cells. /, Double cells with two nuclei from the egg- 

 follicles of Ncpa rim'vm. 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 (gi-anular) mass is circularly enclosed by the nuclear pseudopodia. //, Secreting-cells 

 from the spinning-glands of caterpillars. (After Koi-schelt.) 



sorbed ; the micronucleus grows by the ingestion of substance, 

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



Fia. aoT.— Cells of salivary glands. .-I, At rest. The nuclei arc star-shaped. IS, After stimulation 

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



new macronucleus, which undergo a very considerable increase in 



.size. 



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



1 cy. p. -201. 



