Munson, Organization and Polarity of Protoplasm. 37g 



The nature of astral rays. In the striated eye- 

 muscle of the horned toad, fig. 32, can be seen, still more clearly, 

 perhaps, the persistence of cytoplasmic fibrils; as well as the cha- 

 racter of the material of which the fibrils are composed. There 

 is a beautiful serial arrangement of the cytomicrosomes, embedded 

 in an unstainable matrix, probably more liquid than the micro- 

 somes themselves. 



From what I have been able to see of the fibrils of the nerve 

 cells, I consider them similar to the fibrils of the muscle cells, 

 with the exception that the cytomicrosomes in the nerve fibrils 

 are far more minute, and not so regularly arranged with reference 

 to the other fibrils. In the muscle fibres, the elements are so 

 arranged as to act in unison; while that seems not to be the case 

 in nerve cells. 



As the muscle cell and the nerve cell are specialized, each 

 for the important general physiological properties of contractility 

 and irritability which belong to protoplasm in general, it seems 

 reasonable that we should encounter a fibrillar structure in the 

 unspecialized cytoplasm: For clearly these fibrillar structures in 

 the muscle cell and in the nerve cell belong to the cytoplasm, 

 not to the nucleus primarily, as those would like to maintain 

 who claim that structure is to be looked for in the nucleus only. 



The reticular nature of cytoplasm, as opposed to the purely 

 granulär or the alveolar, becomes apparent in the formation of 

 the aster and spindle, when cells divide, fig. 16, 18, pl. Ib. But 

 it is equally apparent in all of those resting cells, like the ovarian 

 egg of Limulus, fig. 20, and the ovarian egg of Clemmys, fig. n, 

 pl. Ic, where the aster is most distinct. 



There seems to be no valid reason for assuming that the 

 aster is a separate archoplasmic formation which grows out into 

 the cytoreticulum or between the alveoli. On the contrary, the 

 aster in these cells, fig. 20, as well as in the spermatocytes of 

 Papilio, fig. 13, is obviously continuous with the fibrils of the 

 general cytoplasm. The characteristic appearance of archoplasm 

 is due to the fact that the cytomicrosomes are exceptionally small, 

 the fibrils also being too fine to be seen distinctly. Both fibrils 

 and microsomes seem capable of uniting with others into larger 

 Strands, which, of course, become more evidently fibrous as this 

 union advances. The distinctness of the aster and also of cyto- 

 reticulum, is therefore subject to Variation. 



There are good reasons for assuming that the fibrils possess 

 the contractility of the muscle fibre and the irritability of the 

 nerve fibre; for as I have shown, even in Amoeba, the cell may 

 contract in one region and expand in another; these, however, 

 being so coordinated as to lead to a definite forward progression 

 of the movable elements or granules within the cell. It is espe- 



