Xo. 639] 



AMEBIC AN FOLLIC U LIN AS 



ties— ceding the point that these species may well have 

 but a very temporary and artificial value. 



That the species determined from characters of the 

 temporary dwellings of the animal may, however, prove 

 to be real species is indicated by the following consid- 

 erations. 



The bottle or case is a secretion from the surface of 

 the animal, and, as seen by Wright in 1861, the bottom 

 part, or sac, as we call it, is made first, and then the neck 

 or tube added, and finally the lip at the mouth of the 

 bottle. In making the sac the animal flattens its body 

 and assumes the size and the form that the sac will have 

 when it is poured out and hardened all round about the 

 body in this shape, leaving only the blunt anterior end of 

 the body free from secretion, so that the hardened sac 

 comes to have a hole in the anterior end and is a bilater- 

 ally symmetrical product duplicating the form and pro- 

 portions of the animal as if the latter had been cast in 

 the sac as in a mold. The form of the sac is the form of 

 the animal at that period of its life cycle. Subsequently 

 the size, length, spiral ornamentation, if any, and the per- 

 fection of the funnel or lip of the tube are all representa- 

 tions of the habit of the animal in the consecutive phases 

 of the manufacture of the tube. The angle that the neck 

 of the bottle, or tube, makes with the body of the bottle, 

 or sac, is fixed by the degree to wiiich the animal con- 

 tracts its anterior part to rear it up away from the sur- 

 face of attachment and general plane of the sac; the 

 diameter of the tube is that of the head end of the animal ; 

 its circular section is that of the head end; its length is 

 that of the gradual elongation of the entire animal which 

 carries the head end gradually ever farther away from 

 the foot end till the maximum length is attained; the 

 spiral character of the tube, when present, is determined 

 by the rotation of the head end and by the localized and 

 radially differentiated selecting soerotlons ;ni(l ('oiit Tac- 

 tions of parts of the head end; ilw final lip of \\u- tul)(> is 

 added by special change of shape of tin- head vud which 



