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



of the horns. It is most apparent in the tendency toward a pro- 

 portionate reduction of the large apical at the same time with 

 the left antapical in antotomy. A very short apical is usually 

 accompanied by a very short left antapical. The ratios of the 

 antapicals of C. biceps, owing' to their normal disproportion, are 

 subject to extreme variations (figs. 21-24) in comparison with 

 those in species having two large antapicals, as shown in the 

 table. 



The process of autotomy is thus of normal occurrence to a con- 

 siderable extent in deep waters in a large number of species of 

 Ceratiuni and is regulatory in character in the main. 



Not only is autotomy found concidently, as a rule, in both an- 

 tapicals, but it usually preserves approximately their relative 

 lengths. As I have elsewhere shown ( :07) the right antapical is 

 formed by plates 4' " and 5' " of the postcingular series, while the 

 left is formed entirely by the two plates of the more distal antap- 

 ical series. This fact lies at the basis of the general occurrence in 

 many of the species of Ceratiiim of an inequality in the length of 

 the antapicals. The right is usually shorter and its base is always 

 nearer the girdle, while the left is longer and its base is farther 

 removed giving to the organism a fundamental asymmetry. This 

 disproportion of the antapicals is most apparent in the subgenus 

 Biceratium, while in many species of the C. macroceros group 

 the horns are approximately equal, the inequality appearing only 

 on careful measurement. In a few cases in the C. tripos group 

 the right horn is the longer one, as frequently in C. schranhi, and 

 sometimes in C. arcuatum. 



These sustained proportions in the length of the two horns, 

 and not infrequently in that of all the horns, are characteristic 

 of the species and they are preserved in aiitotoyny. An illustra- 

 tion of this appears in C. gallicum (figs. 13-15), C. trichoceros 

 (figs. 16-19), and C. biceps (figs. 21-24), of normal individuals 

 and others which have recently undergone autotomy. The orien- 

 tation of the organism in flotation and in locomotion is obviously 

 profoundly affected by its form and proportions. The preserva- 

 tion of the fundamental inequality of the antapical horns in au- 

 totomy is thus regulatory in character and may indeed be con- 



