AMITOSIS 



39 



D ; t^ 



FIG. 45. Four stages in the mitotic division of a cricket's egg- 

 follicle. 



boundary like the cell-plate, and then never finish by a complete 

 separation. Most frequently the cell forms from two to several nuclei 

 and goes no farther, dying when its duties are finished, which may be 

 a short time in certain follicle cells and stratified epithelia, or may be 

 as long as the life of the animal, as in the case of the muscle cells. 



The commonly received idea, at present, concerning amitosis is that 

 it is a terminal process in the cell's life activities and is a method for secur- 

 ing more nuclear surface for use in forced metabolism or secretion. We 

 have three well-defined cases to examine, out of the many that could be 

 mentioned, to prove that this is highly probable. 



First, the follicle cells of the cricket's ovum show an easily read 

 history that can be interpreted in no other way (Fig. 45). The ovary 

 of this insect, like 

 that of many 

 others, is com- 

 posed of a num- 

 ber of chains of 

 about seven dis- 

 tinguishable ova 

 each. In each 

 chain these are 



continually being added at the top in a small and immature state, while 

 at the same time they are being discharged from the lower end into the 

 reproductive passages in a large and mature condition. The ovum 

 grows many times in bulk and surface area during its descent, the great- 

 est increase occurring in the lower end of the chain. Each ovum is 

 covered with a single layer of flat epithelial cells, the follicle cells, that 

 have the work to perform of transforming the food materials, brought 

 by the blood, into yolk material and passing it on to the ovum, which is 

 storing it up for future use. This layer of cells is fastened to the ovum 

 and accompanies it from the beginning to its discharge. 



The follicle cells increase in size during the descent of the ovum, but 

 not at an equal ratio to the increase of the ovum's surface. Therefore 

 they increase in both numbers and in size to keep the follicular covering 

 complete. The increase in numbers occurs only in the upper end of 

 the chain, and is done by mitotic divisions of the cells. When the 

 ovum is in the lower portion of the chain, these same cells divide by 

 amitosis, which is somewhat incomplete because only the nucleolus and 

 the nucleus divide, the cell body remaining intact in all cases observed. 

 The follicle cells increase in size at this time, however, to keep the 

 follicle large enough to cover the growing ovum. 



Amitosis is clearly not a means of cell multiplication in this tissue. 

 Since it occurs, not only in this well-defined case of rapid metabolism, 



