CELLS AND NUCLEL 267 



In the resting nucleus the nuclear fibre is sometimes replaced 

 by a reticulum, or even by scattered masses and granules of 

 chromatin. 



Growth of the Cells of the Larva. — During the larval stage the 

 epithelial cells of the hypodermis and alimentary canal, as well 

 as those of the salivary glands and fat bodies, do not undergo 

 multiplication, cell-division ceasing with the hatching of the 

 egg or soon after. The rapid growth of the larva results from 

 the increase in the size of the cells, so that when full-grown 

 these attain a magnitude which is quite exceptional. Those of 

 the lingual (salivary) glands frequently measure 150" to 200" 

 (t^t inch), and have nuclei from 50" to 60" in diameter. 



Nuclei of the Salivary Cells. — The nuclei of these gigantic cells 

 are very favourable objects for the study of the resting nucleus. 

 If a larva is opened and immersed for half an hour in Flem- 

 ming's mixture (see p. 94), and then washed for twenty-four hours 

 in 75 per cent, alcohol, the salivary glands can be dissected 

 out, and after staining with Erhlich's hsmatoxylon, the 

 individual cells can be mounted in balsam in the usual way. 

 Such a preparation exhibits the structure of nuclei admirably. 

 Or the cells may be separated after a few minutes' immersion 

 in Flemming's mixture and examined in it; under this treat- 

 ment the nucleus in each cell exhibits a very delicate investing 

 membrane. In some cases I have seen such a nucleus divested 

 accidentally of all ceil protoplasm as a distinct vesicular 

 spheroid, and I have even observed the rupture of the investing 

 membrane, and the escape of the contents — a clear, apparently 

 fluid substance, in which the nuclear threads lie in a more or 

 less dense tangle. 



The nuclear thread consists of large bead-like chromatin 

 granules, varying from 2" to 4" in diameter, flattened where 

 they are in contact with each other, sometimes exhibiting 

 the appearance of a series of cups and balls. The stained 

 granules are invested by an unstained substance, which unites 

 them with each other. Balbiani [126] described a similar con- 

 dition in the nuclei of the salivary glands of Chironomus, and 

 Viallanes [27, p. i6g] states that Henneguy announced to him 



