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ZOOLOGY 



lobe (Fig. 677) divided by a deep median notch into two, 

 each half bearing twelve to fourteen tentacles. On the middle of 

 the oral surface of the latter, close to the median notch, is an oval 

 patch raised up into numerous closely set ridges {organ of Owen). 

 In the male the inner posterior lobe with its ridged organ is only 

 represented by a median posterior body consisting of two oval 

 elevations, each divided into a number of folds {organ of Van der 

 Hoeven). The internal lateral lobes are greatly modified, four of 

 the tentacles on either the right side or the left, usually the latter, 

 being modified to form a structure termed the spadix (Fig. 678), 



ual 



Fig. 677. — Inner posterior lobe of foot of female of Nautilus pompilius, with neighbouring 

 parts of cephalopodium. ow. organ of Owen ; t. one of the tentacles of the outer wing ; 

 vaX. organ of Valenciennes. (After Willey.) 



which is supposed to represent the hectocotylised arm of the male 

 Sepia. It has the form of a large compressed cone formed by the 

 union of the enlarged sheaths of three of the tentacles. The 

 corresponding tentacles themselves are in the adult male enor- 

 mously thickened, and the outer surface of the most posterior {3) 

 is covered with regularly arranged rows of minute pits. A fourth 

 tentacle, much smaller than the others, is closely applied to the 

 outer surface of the organ. In the internal lateral lobe, right or 

 left as the case may be, opposite that bearing the spadix, the 

 latter is represented by a group of four tentacles forming what is 

 termed the anti-spiadix. 



