1908] Eofoid. — Exuviation and Autotomy in Ceratiuni. 373 



trolled by factors analogous to, or the same as those that deter- 

 mine the original inequality of the antapicals at the time of 

 schizogony. The nucleus is oftfen found near the flagellar pore 

 to the left of the center of the midbody and thus nearer to the 

 base of the longer left horn than to that of the shorter right one. 

 The radius of nuclear activity may be one of the factors influenc- 

 ing the inequality both in growth of the horns and in their sub- 

 sequent autotomy and regeneration. 



A striking instance of this regulatory phase of autotomy of 

 the antapicals appears in those species of Ceratiiim such as G. 

 schranki in which the proportionate lengths of the antapicals are 

 reversed, that is the right horn is the longer and the left is nor- 

 mally the shorter one. This reversal of proportions is usnally 

 retained in- these species after autotomy. 



In C. trichoceros the two horns are nearly equal and vary 

 considerably so that either horn may be the longer. In figures 

 16 to 19 are shown respectively a normal individual and several 

 after autotomy, in all of which the proportions of the antapicals 

 are approximately maintained. The apical is also shortened by 

 autotomy but the proportion of the horn removed is less than 

 that dropped from the antapicals, and the ratios which the stump 

 bears to the antapicals are less regular than those between the 

 two antapicals themselves. The following table gives the lengths 

 of the three horns : 



Ceratium iriehoceros, length of horns in transdiameters. 



Apical from girdle right left 



Fig. 16 8.4 14. 13.7 



Pig. 17 3. 4.55 4.65 



Fig. 18 5.8 2.6 2.7 



Fig. 19 1.25 .65 1. 



The location of the planes of autotomy is not a fixed one. In- 

 deed, autotomy may be repeated in the same organism at levels 

 successively nearer the base of the horns (figs. 20 and 24) . It is 

 found in different individuals at all levels from the very tip to 

 the base of the horns. A series showing different levels at which 

 autotomy occurs in C. trichoceros is found in figures 16 to 19, for 

 G. gallicum in figures 13-15, and for C. biceps in figures 21-23. 

 A much more complete series might be made for these or many 



