lOO 



BIOLOGICAL LECTURES. 



Fig. 12. 



matin and other granules evenly distributed through the whole 

 mass of the nucleus. In Fig. 14 a gathering of granules at one 

 point is seen. Fig. 15 shows how perfectly round nucleoli (iil) 

 have been formed. In Fig. 16 we notice that in the interior of 



the nucleolus vacuoles {v) 

 are formed, which grow 

 •^c^-^r "\ bigger and bigger (Fig. 

 17), and finally become 

 so large that the solid 

 substance of the nucleo- 

 lus only appears as a 

 thin membrane, and the 

 nucleolus itself assumes 

 quite fantastic shapes 

 (Fig. 18). Finally the 

 fluid pressure from the interior is so great that the nucleolus 

 bursts and the remains of the membrane are scattered through, 

 the nucleus in the form of irregular plates (Fig. 19). 



This whole process is highly interesting and shows that even 

 in a resting nucleus there is perpetual unrest, not merely chem- 

 ical but also mechanical activity. The term " resting nucleus "^ 

 is a very unfortunate 

 one, which ought to 

 be entirely discarded. 

 We might instead of 

 it, perhaps, use the 

 term nucleus alone, 

 without any adj ective, 

 which is entirely suf- 

 ficient. 



The central canal 



...... - Fig. 13. 



is m the begmning of 



its formation irregular, and often shows bifurcations (Fig. 12, bi)\ 

 but it soon loses all irregularity, and is in the outer cells of 

 the nephridium a perfectly round tube piercing the cell body. 

 This central canal becomes surrounded by a cuticula which 

 is the seat of a new and highly interesting structure. The 

 side canals are also invested by a fine cuticula. 



