No. 3-] MORPHOLOGY OF THE STENTORS. 517 



that they are due to premature, unequal divisions, such as I 

 have described in detail (p. 515). This was certainly the case 

 with pairs 19 and 20, the latter being represented at an early 

 stage of nodulation in Fig. 35, and the former being shown in 

 detail in Fig. 47. 



Another reason for the reconstruction of the meganucleus is 

 that it provides a means of increasing the number of nodes ; 

 for increase does not, so far as my observation goes, take place 

 while the nucleus is in its resting form. Increase of nodes is 

 beautifully displayed in those species where the number of 

 nodes is constant {e.g. in Stylonichia, Onychodromus, and 

 many other Hypotricha), for in these forms the number is 

 exactly doubled after condensation (Balbiani '60, Biitschli '76). 

 In 5. ccEruleus, contrary to the statement made by Balbiani in 

 i860 {p. 77)^ and re-affirmed by him more recently ('81, p. 325), 

 the number of nodes is not regularly increased to double the 

 number in the parent ; yet an increase almost invariably takes 

 place after condensation. ^ Thus the offspring are furnished 

 with nuclei each having a number of nodes considerably 

 greater than half the number possessed by the parent. The 

 nodes are of course smaller. 



Micromiclei. — The division of the micronuclei of Stentor at 

 time of fission has not hitherto been described. By means of 

 sections of 5. ccentletis I have seen micronuclei in mitosis 

 (Fig. 48), but in only a single specimen, although a large 

 number were sectioned in all stages of fission. There is 

 considerable difficulty in making out the micronuclei at all 

 during fission, because they become very transparent and of 

 nearly the same refractive index as the surrounding cytoplasm. 

 Previous to formation of the spindle, the micronuclei enlarge 

 from the normal size of 2)U. to a diameter of 4-5/u, ; at the same 

 time they lose most of their stainability and their high 

 refractive power. The spindles represented in Fig. 48 are 

 evidently at different stages ; the one on the right shows the 



1 I have made only a few observations on this point. In one instance a Stentor 

 in the first stages of fission had a nucleus of 17 nodes; the offspring had nuclei of 

 14 and 15 nodes respectively (pair 15, p. 516). Another case — increase from 

 16 nodes to 20 — has already been mentioned (p. 515). 



