APPENDIX VII 



The following papers are concerned with planarian head frequency: Dugesia doro- 

 toccphala: Child, igixb; Child and Watanabe, 1935a, length of piece, body-level, 

 effect of delay of anterior and posterior section; Child, 191 1/, 1920a, effect of nutritive 

 conditions, size of animal (physiological age), stimulation; Child, igidb, alteration 

 of frequency by KCN; Behre, 1918, alteration by temperature; Buchanan, 1922, 

 alteration by anesthetics; Hinrichs, 1924, alteration by caffein; Rulon, 1936a, 1937, 

 alteration by CO2, H ion, organic acids, and calcium, effects of previous conditioning 

 to CO2 and to H ion; F. S. Miller, 1937, alteration by strychnine. Other species: 

 D. tigrina ( = maculata) : Watanabe, 1935^, length of piece, body-level, effect of delay of 

 anterior and posterior section and section of nerve cords; Planaria lata, now also re- 

 garded as D. tigrina: Sivickis, 1923, length of piece and body-level; P. gonocephala: 

 Abeloos, 1928, length of piece and body-level; Phagocata gracilis: Buchanan, 1933. 



In a lot of pieces as nearly alike as possible as regards length, level of origin, size 

 and physiological condition of parent animals, and reconstitutional environment 

 there may or may not be uniformity of head form, according to conditions. In pieces 

 representing a large fraction of body length and developing in normal environment 

 the uniformity is high — almost or quite 100 per cent normal heads. In pieces repre- 

 senting very small fractions of body length in normal environment the uniformity is 

 also high — almost or quite 100 per cent acephalic. In lots intermediate between these 

 extremes and in pieces subjected to experimental conditions which alter head fre- 

 quencies, a certain range of head forms usually appears in percentages characteristic 

 for the physiological and environmental conditions. Such differences undoubtedly 

 result in part from slight differences in physiological condition and susceptibility of 

 different individuals and in part from unavoidable variations in length of pieces and 

 level of origin. Frequencies of the different head forms can be tabulated numerically 

 or as percentages, and a general comparison made from these data; but for graphic 

 presentation and comparison it is convenient to have a value for the head frequency of 

 a lot rather than the individual frequencies. Such values, adequate for the compara- 

 tive purposes for which they are used, are readily obtained as follows: numerical values 

 are assigned to each of the head forms — for example, normal, 100; teratophthalmic, 

 80; teratomorphic, 60; anophthalmic, 40; acephalic, 20. From these values an index 

 for the lot is obtained by multiplying the number of cases of each head form by the 

 numerical value for that form and dividing the sum of these products by the number of 

 pieces in the lot; or, if the frequencies are expressed in percentages, multiplication of 

 the percentages by the numerical values and division of the sum of the products by 100 

 gives, of course, the same result. The procedure is clear from the formula 



_ ioo»5 + 8o«4 + 6o»3 -j- 40/72 + 2o;7i 

 ~ N ' 



745 



