48 GEXERAl. SKETCH OE THE CELL 



ill life, the network is loose and open, and appears to consist of more 

 or less completely separate threads (Fig. 9). In tlie cells of colum- 

 nar epithelium, the threads in the peripheral part of the cell often 

 assume a more ox less parallel course, passing outwards from the 

 central region, and giving the outer zone of the cell a striated appear- 

 ance. This is very conspicuously shown in ciliated epithelium, the 

 fibrillne corresponding in number with the cilia as if continuous with 

 their bases (Fig. 17).' In nerve-fibres the threads form closely set 

 parallel fibrilla? which may be traced into the body of the nerve-cell; 

 here, according to most authors, they break up into a network in 

 which are suspended numerous deeply staining masses, the " chromo- 

 philic granules" of Nissl (Fig. 20).'-^ In the contractile tissues the 

 threads are in most cases very conspicuous and have a parallel course. 

 This is clearly shown in smooth muscle-fibres and also, as Ballowitz 

 has shown, in the tails of spermatozoa. This arrangement is most 

 striking in striped muscle-fibres where the fibrill?e are extremely well 

 marked. According to Retzius, Carnoy, Van Gehuchten, and others, 

 the meshes have here a rectangular form, the principal fibrillae having 

 a longitudinal course and being connected at regular intervals by 

 transverse threads ; but the structure of the muscle-fibre is probably 

 far more complicated than this account would lead one to suppose, 

 and opinion is still divided as to whether the contractile substance 

 is represented by the reticulum proper or by the ground-substance. 



Nowhere, perhaps, is a fibrillar structure shown with such beauty as 

 in dividing cells, where (Figs. 21, 31) the fibrillae group themselves 

 in two radiating systems or asters, which are in some manner the 

 immediate agents of cell-division. Similar radiating systems of fibres 

 occur in amoeboid cells, such as leucocytes (Fig. 49) and pigment- 

 cells (Fig. 50), where they probably form a contractile system by 

 means of which the movements of the cell are performed. 



The views of Butschli and his followers, which have been touched 

 on at p. 25, differ considerably from the foregoing, the fibrillae being 

 regarded as the optical sections of thin plates or lamellae which form 

 the walls of closed chambers filled by a more liquid substance. 

 Butschli, followed by Reinke, Eismond, Erlanger, and others, inter- 

 prets in tlie same sense the astral systems of dividing cells which 

 are regarded as a radial configuration of the lamellae about a central 

 point (Fig. 10, B). Strong evidence against this view is, I beheve, 



1 The structure of the ciliated cell, as described by Engelniann, may be beautifully demon- 

 strated in the funnel-cells of the nephridia and sperm-ducts of the earthworm. 



- The remarkable researches of Apathy ('97) on the nerve-cells of leeches have revealed 

 the existence within the nerve-cell of networks far more complex and definite than was 

 formerly supposed, and showing definite relations to incoming and outgoing fibrillce within 

 the substance of the nerve-fibres. 



