364 University of California Publications in Zoology. [Vol.4 



at the surface, and steeper on the proximal face, which sink into 

 the substance of the wall and sever it upon all sides. The super- 

 ficial location of the troughs suggests the agency of the extra- 

 membranous plasma in bringing about a local resolution of the 

 cellulose wall. I have found no indications of local solution on 

 the inner face of the wall below the groove. There is no evidence 

 of a withdrawal of the distal plasma from the outer part of the 

 horn to the region proximal to the plane of section in individuals 

 exhibiting the early phases of autotomy. Isolated horns found in 

 the plankton with the proximal stump conforming to the section 

 plane formed by autotomy, often contain a normal plasma core. 

 The line of breakage formed by fracture is, on the other hand, 

 usually an irregular ragged line often oblique to the axis of the 

 horn. 



(6) Regulatory character of autotomy. — One cannot fail to 

 be impressed with the fact that a large proportion of the in- 

 dividuals exhibiting mutilation of the horns have either ( 1 ) both 

 antapicals, or (2) all three horns cut off. This appears far in 

 excess of the proportion demanded by the chances of accidental 

 breakage. For example in a collection taken eleven miles off 

 Point Loma on January 12, 1905, from a depth of 60 fathoms, a 

 large number of individuals exhibit mutilation and of the first 

 thirty-five observed in searching material with a mechanical stage 

 no less than twenty-nine had both antapicals cut off, and twenty- 

 six of these also had the apical similarly foreshortened. 



The occurrence of individuals in which one or two horns have 

 undergone autotomy while the other two or the third are still in 

 the process is not unusual. An instance of this sort is shown in 

 figure 24 of C. biceps, in which the apical is short, possibly as a 

 result of recent autotomy, and the left antapical is nearly sev- 

 ered by two separate and distinct but adjacent section planes at 

 a distance posterior to the girdle approximately proportional to 

 the foreshortened apical horn. Such cases are suggestive of an 

 approximation in the time of the autotomy of the two main horns 

 of this species. 



With a view of determining the extent and character of the 

 processes of autotomy and of regeneration in a typical collection 

 from deep water I made an examination of the plankton taken 



