ANALYSIS OF FORM REGULATION. 1 65 



The process of regulation ceases in the anaesthetic before the 

 degree of development attained in water is reached. The head 

 remains of smaller size in proportion to the size of the piece, the 

 " auricles " on the sides of the head, which in this species are 

 normally long and pointed, remain short and blunt, the new 

 pharynx attains only a fraction of the size attained in water, 

 and intestinal regulation, with the exception of the degeneration 

 of the smaller intestinal branches in many cases, does not occur 

 to any appreciable extent until the animals begin to move about 

 actively. 



These results are sufficient to show that the method affords a 

 means of separating more or less completely in time certain 

 regulatory processes which under normal conditions occur 

 together, and thus of determining in some degree their relations 

 to each other, and in the cases of change of shape and develop- 

 ment of the tail their relation to movement and use of parts. 



Another most interesting difference between the pieces in 

 anaesthetics and those in water is the relation between regenera- 

 tion in the stricter sense and redifferentiation. In certain pieces, 

 which in water form the whole head back as far as the eyes by 

 regeneration of new tissue, only the more anterior portions of the 

 head are formed in this way in anaesthetics. In this respect 

 alcohol and ether differ to some extent : in ether apparently less 

 regeneration and more redifferentiation than in alcohol occurs, 

 and in some cases in ether only the extreme tip of the head is 

 regenerated, all other parts being the result of redifferentiation. 

 A case of this kind is figured in my paper referred to above 

 ( 9, Figs. 14-16). As regards this point the process of regu- 

 lation resembles that occurring after long continued starvation, 

 but the substitution of redifferentiation for regeneration is even 

 more complete in the anaesthetics than after starvation. 



IV. The Effect in Relation to the Size of the Piece. 

 In general a larger piece is necessary for the production of a 

 whole, or anything approaching a whole, than in water. Within 

 certain limits the death-rate increases as the size of the piece 

 decreases. Regulation is retarded to a much greater extent in 

 smaller than in larger pieces. In smaller pieces the formation 



