1908] Eof Old.— Exuviation mid Autotomy in Geratium. 363 



2. It is more frequently found in collections from deep water 

 (50-100 fathoms) tlian in those from the surface. It is also 

 more abundant in collections of tropical fades occurring at San 

 Diego than it is in those made up of species of more northerly- 

 distribution. Not infrequently, especially in the winter of 1904, 

 the plankton collections taken off San Diego were unusually rich 

 in species characteristic of the warmer seas, and at such times the 

 proportion of mutilated Geratium was unusually large. 



Instances of autotomy of the horns of Geratium occur also in 

 surface collections made off San Diego. There is no evidence at 

 hand to show whether these cases originate in these levels or are 

 brought to the surface by the upwelling of colder water from 

 lower levels a phenomenon known to occur along the California 

 coast (see Holway '06) or by the aspiration of water from lower 



sec. pij 



sec. plJ 

 Fig. 20. — Dorsal view (somewhat oblique) of Geratium protuberans in 

 the process of autotomy. X 360. Supplementary sketches indicate the 

 form of the section planes. 



Abbreviations — chr., ohromatophores ; n., nucleus; sec. pi., section plane. 



levels in vortices formed between currents of tidal or oceanic 

 nature flowing in opposite directions, as shown by Nathanson 

 ('06). 



3. Evidence of autotomy. — (a) Formation of section planes. 

 The horns are cut off by the circular clefts, often though not al- 

 ways quite regular in form and transverse to the axis, which en- 

 circle the horns and form (fig. 20) wide V-shaped troughs, wider 



