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THE AMERICAN NATURALIST [Vol. LV 



assumes a mushroom form and secretes from its under 

 surface. At any one period of making of tube the tube 

 expresses the resultant of the two components, contrac- 

 tion and secretion by the body at that moment. 



While the entire animal never has the shape of the 

 tube, yet each part of the tube exactly fits the head end 

 of the animal as it progresses away from the foot in co- 

 ordination with the elongation of the whole animal. The 

 completed structure represents a solidification of the 

 form rhythms of the animal as does the shell of a gas- 

 teropod or the successive exoskeletons of a lobster or the 

 hard envelope of a rhizopod, and differs from most of 

 these chiefly in that the animal only temporarily assumes 

 the forms expressed by the dwelling, and later lives freely 

 movable in the dwelling and capable of leaving it by 

 simply detaching the foot-end from the bottom of the sac. 



How precisely the bottle represents the animal was 

 seen in one instance when camera drawings of two suc- 

 cessive bottles made by the same animal exactly coin- 

 cided. If, then, the different shapes and sizes of bottles 

 do not mean different species, it is because the different 

 activities and forms of these animals are not specific, but 

 only varietal or individual differences, or differences due 

 to changing conditions, such as food, or to different suc- 

 cessive internal states connected with internal rhythms. 

 In ignorance of the possible changes of form any animal 

 may go through, we may, for practical purposes, follow 

 Carl Dons in describing the bottles as expressions of 

 forms that mai/ be specific in value. 



Of the anatomical characters in Folliculina that may 

 be made use of in classification, the nucleus has been em- 

 phasized by Dons, who would regard a moniliform nu- 

 cleus as the attribute of one group of folliculinas as rep- 

 resented by Mueller's original species, while all others 

 have a siii-lc lobcd ^\m])\v imclciis. l^ut this is of no 

 avail, t'oi- in tht' i\vs\ place, the folliculina thoroughly 

 stu(li.'<l l)y .\ir.l)iiLs had inonilir.)iTii nucleus but its dwell- 

 ing can not at all be confounded with that of Mueller's 



