PHYSIOLOGY OF RECONSTITUTION OF PLANARIA LATA. 115 



forms are at once distinguishable by these differences in pigmenta- 

 tion. Moreover, the general color effect to the naked eye in the 

 mid-western form is a light grayish brown, mottled or dappled, 

 while in P. maculata the brown tint is much deeper and more uni- 

 form. In P. maculata a light median longitudinal stripe is almost 

 invariably present (Fig. 2), while the mid-western form usually 

 shows an obscure dark median stripe (Fig. 1). 



As regards shape of body, the mid-western form is distinctly 

 broader in proportion to length than P. maculata (cf. Figs. 1 

 and 2). This difference is evident during locomotion as well as 

 at rest. The cephalic lobes are apparently slightly less developed 

 and the digestive tract appears more highly branched in the mid- 

 western form than in P. maculata. 



As regards motor behavior, also marked differences appear. 

 The mid-western form is distinctly more sluggish, reacts more 

 slowly, and progresses less rapidly than P. maculata. Similar 

 differences in reaction to food exist. P. maculata can be collected 

 by placing pieces of meat in the water in localities where the 

 species occurs. As the extractives diffuse, the animals will come 

 to the meat from a distance of several inches in standing water and 

 from greater distances in flowing water. The mid-western form 

 can not be collected in any considerable numbers in this way be- 

 cause only those animals immediately about the meat react. In 

 feeding stocks in the laboratory it has been found necessary to 

 grind the meat and spread it over the bottom of the container, 

 instead of placing pieces at intervals of two or three inches, as has 

 been the practice with P. dorotocephala and P. maculata. 



All these differences persist unchanged in stocks of the two 

 forms kept in the same water and under the same conditions in 

 Chicago. This is true, not only as regards the original individuals, 

 but also as regards young animals resulting from fission or recon- 

 stitution of pieces and animals hatched from eggs. Reconstitu- 

 tion experiments with the two forms also show certain character- 

 istic differences in head frequencies. 



These differences are unquestionably sufficient to make it evi- 

 dent that the mid-western form is not P. maculata. However, 

 since the morphological characteristics of the organ complex of 

 the genital atrium, and particularly the copulatory organ, are com- 



