44 



GEXEK.U. SKETCH Of THE CELL 



microsomes in certain cases. In nian\- Protozoa, for example, a fine 

 alveolar structure ma\' be seen in the lixini;- ])rotoplasm ; and Flem- 

 ming as well as many later observers has clearly seen fibrillar struc- 

 tures in the livinj;- cells of cartilage, epithelium connective-tissue, and 

 some other animal cells ( Fii;". 9). Mikosch, also, has recently described 

 ^'■;v?/////<rr threads in living plant-cells. 



Almost et[uallv conclusive is the beautifully regular arrangement 

 of the hbrilhr in ciliated cells (Fig. 17, Engelmann), in muscle-fibres 

 and nerve-tibres, and especiallv in the mitotic figure of dividing cells 







€-^ 





Fig. 18. — Cells of the pancreas in Amphibia. [Mathews.] 



A-C. Necfiiriis : D. Nana. A and B represent two stages of the " loaded " cell, showing 

 zymogen-granules in the peripheral and fibrillar structures in the basal part of the cell. C shows 

 cells after discharge of the granule-material and invasion of the entire cell by fibrillse. In D por- 

 tions of the fibrillar material are coiled to form the mitosome (" paranucleus " or " Nebenkern "). 



(Figs. 21, 31), where they are likewise more or less clearly visible 

 in life. A very convincing case is afforded by the pancreas-cells 

 of Nectnrits, which Mathews has carefully studied in my laboratory. 

 Here the thread-work consists of long, conspicuous, definite fibrillae, 

 some of which may under certain conditions be wound up more or 

 less closely in a spiral mass to form the so-called Nebenkern. In all 

 these cases it is impossible to regard the thread-work as an accidental 

 coagulation-product. In the case of echinoderm eggs, I have made 

 ('99) a critical comparison of the living structure, as seen under powers 



