1908] Kofoid. — Exuviation and Autotomy in Ceratium. 375 



therefore of the resistance which the molecular friction of the 

 water affords to the sinking of the body. 



Ostwald ( :03) has defined specific surface as the ratio of 

 absolute surface to absolute volume. Computation of the actual 

 surface and volume of a normal individual of G. gallicum and 

 of the horns beyond a plane of autotomy midway in their length 

 gives the following results, when S and V represent respectively 

 the surface and volume before autotomy and s and v the corre- 

 sponding measurements of the horns beyond the plane of section. 



,^- > -f,-^^ or 265 > 210.5. 



The decline in specific surface is thus about 20.5%. Applying 

 this to Ostwald 's ( :03 ) computations of the changes in molecular 

 friction attendant upon changes in temperature we find that an 

 increase of 20.5% in the molecular friction found in sea water at 

 20% would be equivalent to a drop in temperature of 7.43°. In 

 other words, a normal C. (jalliciim before autotomy floating in 

 water at 20°, would, other things being equal, be equally adapted 

 to flotation in water at 12.57 by the autotomy of its horns mid- 

 way in their length. Without autotomy its specific surface upon 

 the lowering of the temperature would be in excess of its needs 

 and would tend to maintain the organism in levels nearer the 

 surface when once it entered them. 



The cause of autotomy is not easily determined in view of the 

 complex and largely unknown chemical and physical factors in- 

 volved. Nevertheless the data of its occurrence are sugjiX'stive 

 of the agency of certain of these factors, which may, moreover, 

 be tested by experiment. Ccraiiiim presents in its structure cer- 

 tain conditions peculiar among unicellular organisms, namely 

 that of three distally projected protoplasmic horns which secrete 

 upon their surface a continuation of the cellulose wall of the mid- 

 body. The synthetic processes of the cell go on only in the 

 presence of the nucleus. The distance from the nucleus at which 

 the metabolic processes involved in the secretion of cellulose can 

 go on are possibly affected by temperature. Whether or not this 

 results from the relation of temperature to the velocity of chem- 

 ical reactions, we do not know. The facts are that in warmer 

 waters the horns of practically all species are projected to a pro- 



