1908] Eofoid. — Exuviation and Autotomy in Geratium. 379 



yet attained the length, thickness or surface markings character- 

 istic of the species. This growth is apparently not a prolonged 

 process, but one abruptly made, in like manner to the original 

 growth of the horns. The evidence for this lies in the fact that 

 the newly found portions of the wall are of approximately uni- 

 form texture throughout their length. They are also formed 

 coincidently, since they are of similar texture on the three horns. 

 Observations on many instances of regeneration in many species 

 of Ceratium bear out the statement here made concerning their 

 rapid and coincident formation. In figures 28 and 29 are shown 

 similar instances of distal regeneration of the apical horn in C. 

 lamellicorne and C. reticulatum spirale. 



Regeneration proceeds in a slight measure, however, centri- 

 fugally from the stump of the horn. This is seen in the fact 

 that occasionally individuals are found in which the protoplasm 

 is naked distally or in which the distal part of the newly formed 

 section of the horn is more delicate than the proximal. Such dif- 

 ferences are, however, relatively insignificant and temporary. 



3. Regenerative growth independent of autotomy. — In species 

 having antapicals with closed tips such as those of the G. tripos 

 and G. furca group I have found some evidence of distal exten- 

 sion of the antapical horns without preceding autotomy. In 

 figure 26 is seen an individual of C. arcuatum which has under- 

 gone distal autotomy, and in figure 25 an instance of distal re- 

 generation of the closed tips, apparently after autotomy. In the 

 course of my examination of collections I have found numerous 

 cases of subsequent distal regeneration of new tips after such 

 distal autotomy in various species of the G. tripos group. 



In a plankton collection taken July 12, 1904, in a haul from 

 75 fathoms to the surface there were a large number of Geratium 

 divaricatum in which there was rene"wed centrifugal growth at 

 the tips of the closed antapicals and occasionally also of the tip 

 of the apical as shown in figure 31. In some cases all three horns 

 had renewed distal centrifugal growth, in others only the apical, 

 and in still others either one or both of the antapicals. In no 

 observed case, however, does the growth reach an extent which 

 carries any of the horns beyond the normal range of variation in 

 this species. This growth in G. divaricatum takes place at the 



