1908] Kofoid. — Exuviation and Autotomy in Ceratium. 365 



with a No. 20 silk net, which presumably retains most of the 

 small and short-horned forms of Ceratium, from a depth of nine- 

 ty-six fathoms off San Diego, June 29, 1905. This catch was 

 made by towing at this depth from a drifting boat for about 20 

 minutes. The net is in action, however, during both the descent 

 to and ascent from this depth. The net presumably obtained a 

 large proportion of its catch from lower levels but also filtered 

 some water from the intervening and surface levels. 



Samples withdrawn from the collection were examined with 

 the aid of a mechanical stage and all individuals of all species of 

 Ceratium were recorded with reference to their approach to the 

 norm of the species as observed generally in oceanic plankton off 

 San Diego. The length of the horns was measured in trans- 

 diameters of the midbody at the girdle of the individual under 

 observation, and the extent of regeneration, if present, was re- 

 corded for each of the horns in the same units. By this method 

 the proportionate, compensatory, assimilative or regulatory char- 

 acter of the two processes of autotomy and regeneration of the 

 horns is expressed quantitatively. Since every individual was 

 recorded all elements of personal selection are eliminated. 



The results are very striking in that they exhibit the extent 

 to which autotomy and regeneration occurred within the limits 

 between a depth of ninety-six fathoms and the surface and also 

 the degree to which the processes of autotomy and regeneration 

 are regulatory. 



The first 125 individuals of Ceratium were recorded as shown 

 in the accompanying table. 



