io8 C. M. Child. 



This case differs from that of Stenostoma in which the posterior 

 end alone is the chief organ of attachment. Reference to my paper 

 on Stenostoma (Child, '02) will show clearly how the character- 

 istic differences of external form betewen Stenostoma and Lepto- 

 plana may be correlated with the differences in the mechanical 

 conditions to which the tissues are subjected. 



My experiments also indicate that the use of the anterior por- 

 tions of the lateral margins in drawing the body forward consti- 

 tutes a factor in their development. In consequence of these char- 

 acteristic, frequently repeated movements these parts are sub- 

 jected to characteristic physical conditions, which, like the longi- 

 tudinal tension, must exert some influence upon the arrangement 

 of the cells and tissues. 



Anyone who observes the creeping movements of different poly- 

 clads cannot fail to note the close correlation between the gen- 

 eral outline of the body and the character of the movement. In 

 general the forms which advance in a definite direction are more 

 slender than those like Stylochus whose movements are very in- 

 definite in direction. In the last mentioned form lateral move- 

 ment occurs almost as often as longitudinal, a part of the body- 

 margin being advanced and the other portions drawn up to it by 

 contraction. The breadth of the body is almost as great as the 

 length in Stylochus. I am forced to the belief that the forms of 

 the various species are determined in greater or less degree by the 

 conditions of tension, resulting from swimming and creeping 

 movements, to which the tissues are subjected. The experiments 

 to be described afford strong support to this view. 



THE LIMITS OF REGENERATION. 



This section includes merely a brief preliminary statement 

 concerning the power of regeneration in Leptoplana. The phe- 

 nomena will be treated more at length in other connections. 



Complete anterior regeneration never occurs in Leptoplana 

 when the cephalic ganglia are removed. Removal of all portions 

 of the head anterior to the ganglia and even including the anterior 

 part of the ganglia Is followed by rapid and complete regenera- 

 tion. 



