1 62 RALPH S. LILLIE. 



develops on its own account. Cases of compensatory regulation, 1 

 i. e., where the rate of regeneration is greater the greater the 

 number of the missing parts, may be understood as due to the 

 more complete removal of the inhibiting influence exerted 

 normally by those parts. In other cases one region may promote 

 or reinforce the growth or development of another region; the 

 nervous system appears to have this relation to regeneration in a 

 number of cases; the presence of sense-organs promotes re- 

 generation in Cassiopsea; the intestinal tract has a similar 

 influence in planarians. 2 



Some of the more suggestive parallels between regenerative or 

 growth processes and the behavior of combinations of filament- 

 forming metals have already been pointed out. The formation 

 of precipitation-filaments from one metal is inhibited by the 

 contact of another metal of higher solution-tension. Hence an 

 iron wire connected with a piece of manganese, aluminium, zinc, 

 or magnesium remains free from filaments for a considerable 

 distance from the region of contact. If a piece of such wire be 

 isolated by cutting, it immediately develops filaments. Simi- 

 larly iron wire connected with one of these metals through a 

 short copper wire develops no filaments; cutting the connecting 

 wire immediately initiates their formation. These instances are 

 sufficient for illustration of this kind of effect. The precise 

 results obtained vary with the special nature of the conditions, 

 and may be controlled at will by the experimenter. 



The reverse class of cases where the formation of filaments is 

 promoted, instead of inhibited, may be illustrated by a strip of 

 zinc in contact at one end with a piece of carbon, platinum, 

 copper or iron. Filaments are formed from all parts of the zinc 

 surface, most rapidly near the region of contact. If then part 

 of the zinc is severed from its connection with the other metal 

 the development of filaments from the isolated part is at once 

 checked; similarly with the whole strip if the platinum or copper 

 is removed. One might compare the influence of the latter 



1 Cf., e. g., Zeleny's work on brittle stars and other forms. Jour. Exper. Zool., 

 1904, Vol. 2, p. i. 



2 Instances of the influence of the nervous system and sense-organs have been 

 already cited; for the case of the intestinal tract, cf. Bardeen, Amer. Journ. Physiol., 

 1901, Vol. 5, p. i. 



