SUMMARY AND CONCLUSION 237 



ulcs be only different modifications of the same element, a presump- 

 tion certainly exists that they have such powers. When we extend 

 this comparison to the cytoplasm, the ground becomes more uncer- 

 tain. It seems well established that the cytoreticulum is of the same 

 nature as the linin-network. If this be admitted, we are led to accept 

 on a priori grounds that some at least of the cytomicrosomes are not 

 artefacts, but morphological bodies comparable with those of the linin 

 and chromatin networks, and like them capable of growth and division. 

 This conclusion is, as yet, no more than a somewhat doubtful inference. 

 In the centrosome, however, we have a body, no larger in many cases 

 than a " microsome," which is positively known to be a persistent 

 morphological element, having the power of growth, division, and 

 persistence in the daughter-cells. Probably these powers of the cen- 

 trosome would never have been discovered were it not that its stain- 

 ing-capacity renders it conspicuous and its position at the focus of 

 the astral rays isolates it for observation. When we consider the 

 analogy between the centrosome and the basichromatin-grains, 

 when we recall the evidence that the latter graduate into the oxy- 

 chromatin-granules, and these in turn into the cytomicrosomes, we 

 must admit that Brucke's cautious suggestion that the whole cell 

 might be a congeries of self-propagating units of a lower order is 

 to-day not entirely without the support of facts. 



LITERATURE. VI 



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