40 



HISTOLOGY 



but also in many others, we have some right to connect it with these 

 processes and to infer that its principal object is to provide increased 

 nuclear surface as quickly and with the least expenditure of energy 

 possible. 



A second example is described on page 90 (see Fig. 87). Here, 

 again, the nucleus divides by mitosis, while the cells are increasing in 

 number in the primitive muscle regions. When the cells are sufficient 

 in number and begin to form nbrillae, the nuclei rapidly multiply by 

 amitosis, probably to afford more nuclear surface to the growing cell, 

 which is now secreting the heat- and motion- producing substance in in- 

 creasing quantities. 



The third case that we shall examine is a very common one, and is 

 found in nearly all stratified epithelia, especially in the higher vertebrates 



(Fig. 46). Here, as in the fol- 

 licle cells of insects, the nucleus 

 divides by mitosis to increase 

 the number of cells; but it 

 changes to amitosis, without a 

 division of the cell body in the 

 latter part of the cell's life. 

 Again, the probable object is to 

 enlarge the nuclear surface for 



FIG. 46. Amitotic division in the middle stratum increased metabolism, the foi- 



mation of kera tin in this case. 

 Strangely enough the special- 

 ized parts of this epithelium that produce certain oils and scents show 

 no signs of amitosis in their later stages of secretion and degenera- 

 tion (see Chapter XX). 



The above cases could be multiplied indefinitely. As was seen in 

 the preceding part, mitosis is also used in them for other purposes than 

 growth ; but we are now confronted with the question, can amitosis be 

 used for any real growth purposes? 



Opposed to the preceding general ideas as to the meaning of amitosis 

 we find the conclusions of Child (1907) and others who, in very recent 

 papers, apparently show that amitosis occurs very extensively as a fac- 

 tor in the growth and regeneration of many young and unspecialized 

 tissues, including even the reproductive tissues. This is described in 

 tissues from most of the principal groups of animals. 



The observations on which these descriptions are based are as yet 

 "somewhat fragmentary" according to the chief observer, Child (1907). 

 And yet we must recognize that if they contain any truth at all they must 

 contain a great mass of facts that will seriously conflict with the pre- 

 vailing ideas. Meves' observation on the reproductive cells of the 



