VARIATION AND REGENERATION. 



811 



its hold upon the shell, Nautilus can project its body from the shell with a darting 

 movement and protrude the buccal cone so as to seize hold of its food. I have seen 

 it seize a pra^\^l between its jaws in this way, and it would not be a difficult matter 

 for a female to bite into the hood of a male. However this may be, the point to 

 which I desire to draw attention is that the wounds heal up at the edges, but the 

 parts are not regenerated. 



Table of Variations. 



Amphioxus is another example of a relatively fixed type which presents little range 

 of variation, and less power of regeneration. Perhaps Chiton is another. 



Sometimes the sheaths of the tentacles become perforated at some part of their 

 length, and the tentacle may then issue from the adventitious orifice instead of from 

 the apical orifice. 



Not seldom among the shells of N. pompilius which are washed upon the reefs 

 of New Guinea specimens are found in which the umbilicus is incompletely closed'. 



' I have figured some examples of this umbilical aberration in Quart. J. Micr. Set., sxxix., figures ou 

 PI. 13, 1896, pp. 227—230. 



w. VI. 106 



