56 



ANDREWS. 



and physiological isolation gained for different areas or sub- 

 stance organs by pellicular formations of ectosarc. When looked 

 at from the standpoint of protoplasmic habit, they must be 

 regarded as continuous with the protection by ever increas- 

 ingly complex and complete ectosarcal areas of all portions of 

 the organism not concerned in the ingestion of food ; and finally, 

 with the systems of protective apparatus which, as tactile, and 

 as offensive and defensive structures, guard at last even those 

 weaker regions. The original formation may undergo more 

 or less subsequent modification by secretion, or deposit, within 

 or about it, of non-living material, such as chitin, silica, or 

 the like. The actual living substance may be withdrawn, or 

 may be gradually atrophied. In many cases it is impossible 

 to say whether it is still present at a given stage, or whether 

 it has been withdrawn or atrophied. 



The function of secretion does not inhibit in the substance, 

 nor imply its renunciation of, typical contractile characters ; 

 on the contrary, the latter may accompany the former to a 

 marked degree. There is even strong reason for supposing 

 that the function of contractility is always correlated with more 

 or less excretion from the functioning substance, and here again 

 it must be urged that it is most difficult for us to draw a line 

 as yet between substance secretions and substance excretions. 



For we are dealing always, it must be remembered, with a 

 complex series of alveolar structures, not with one alone, as 

 Butschli's, for instance. Rhythmic, or irritably responsive, 

 contraction most frequently accompanies a secretive function, 

 and typical ectosarcal characters are very favorable to this 

 state of things. By contraction, interalveolar vesicles may 

 readily be emptied into the larger inclusions of Biitschli, and 

 from these, which are storehouses of secretions as we know 

 them, contractions of their interalveolar material pour the 

 fluids. In strict sense, though not in common usage, the sub- 

 stance produced by areas and organs should be called excretions 

 when exuded from those places of formation, and secretions so 

 long as they are considered in situ, although here they may be 

 again strictly excretions of the living substance, that is, of the 

 continuous substance. 



