■ \')S riiirdsHij of Calif oniid Publiralioiis iv ZooJof/ij. [Vol.4 



\VL'll-(leveli)l)ed pores. They did not ijiei'fiv K'''i'l'i"'ly ^"*° ^^^ 

 thin plates ii])(iii which llicy abutted but dropi)rd oil' abruptly at 

 the suture lines. Their thickness w;is not less th;ui five tunes 

 that of the adjacent new phites. The thin-wjdlcd plates of the 

 anterior schizont included tin' four a[>icals, l'-4' and [)recin^'iilars 

 3" and 4" They were uniformly thin and hyaline and tbi-ir 

 pores were scarcely visible. The plates of the apical scrii's were 

 least regenerated, and were, indeed. Iiai'ely foi'nied at the di.stal 

 end of the apical horn. 



The condition of all three horns in this s])eeinien was indica- 

 tive of their recent autotoniy. In (' arriialuni in normal condi- 

 tion (fig. 25) the antajticals are much lonjzer than in this speci- 

 men and have pointed elt)sed tips. The api<'al is also noi-mally 

 of at least twice the length in this individual. In this specimen 

 all three horns are abnormally shoit and the anta|)ieals aie 

 abruptly truncated and open. The three horns are. moreover, 

 roughly .still in tlie normal proportions of the horns in arcunfimi 

 to which species this individual appears to belonir. The autotomy 

 of the two antapicals is here attended by a propoi'tionate reduc- 

 tion in the length of the apical. 



The conditions here presented by this specimen unquestion- 

 ably indicate a process of exuviation in which a thecal wall of 

 senile character is in the piocess of being dropped off plate by 

 plate and replaced by a new wall of delicate texture. The or- 

 ganism does not abandon its old theca as do (ih iimlinium and 

 Gcniyauhts, but drops it off piece-meal. Of the fifteen main 

 plates of the theca but four here remain of the old type. 



It may be significant in this specimen that all four of these 

 plates belong to the aiitcriar .segment. It is thus possible tliat 

 this exuviation attended schizogony and that the anterior ses- 

 ment shed its plates and regenerated new ones of a type similar 

 to those forming on the posterior segment as a result of the for- 

 mation after schizogony of new plates over the whole body, be- 

 neath the old on the anterior segmt'ut as well as over the posterior 

 segment. The formation of the new plates beneath the old on 

 the anterior moiety would result in the release and fallinu' apart 

 of the superimposed old plates of the anterior segment. It seems 

 probable also that autotoniy of the horns of a i'(>gnlative or com- 



