404 C. M. CHILD 



have already been published in full, the results of various other 

 experiments including some of those recorded in the present paper 

 have appeared in brief preliminary form (Child, '11 a), and fur- 

 ther experiments on the action of various anesthetics are in 

 progress. These experiments have demonstrated that the var- 

 ious types of anterior end produced by the action of external 

 chemical and physical agents are the same as those which arise 

 in relation to length of piece, region of body, and other physio- 

 logical conditions. 



In most of the work along this line five types or categories of 

 anterior end have been distinguished (Child, '11 a, '16) : normal, 

 a head with two distinct eye-spots, lateral cephalic lobes, and 

 pointed tip, as in nature; teratophthalmic, a head of normal 

 shape, but with eye spots more or less approximated, to the 

 median line, often unequal in size, or more or less completely 

 fused in consequence of failure of the median region of the ceph- 

 alic ganglion to develop completely (Child and McKie, '11); 

 teratomorphic, a more extreme degree of inhibition of the median 

 region, showing a single or completely fused eye spots in the 

 median line and cephalic lobes more or less approximated at the 

 front of the head, in consequence of incomplete development of 

 the median region of the tip; anophthalmic, with a distinct out- 

 growth with rudimentary ganglion, but without eye spots; aceph- 

 alic or headless, with mere healing of the wound and no outgrowth. 

 The term 'head-frequency' has been used to indicate the fre- 

 quency with which these different types of anterior end occur 

 in a given lot of pieces. 



The present paper is concerned with the influence of certain 

 physiological conditions upon head-frequency. The methods of 

 experimental procedure are essentially similar to those described 

 in earlier papers. Each lot of animals used consists of individuals 

 of the same length from a single laboratory stock kept under 

 known conditions of nutrition, temperature, etc., for at least 

 several weeks before the experiment. Each lot of pieces isolated 

 from such animals represents as nearly as possible a given fraction 

 of length and a given region of the body. In all series tabulated 

 except one, the experimental lots consist of fifty pieces each and 



