128 C. M. CHILD 



At the highest temperature all of the pieces form wholes: at 

 a temperature of 20° 22 per cent, and at 10° 44 per cent remain 

 tailless. There is some difference in the amount of new tissue 

 in the tailless forms : the usual type at 20° is shown in figure 36 and 

 that at 10° in figure 37, though some animals like figure 36 occur 

 at 10° and some like figure 37 at 20°. In all of these cases regula- 

 tion at the posterior end is almost completely inhibited. The 

 growth of new tissue does not proceed far beyond closure of the 

 wound and the region is not used as a tail by the animal. The 

 difference in this respect is striking. These tailless forms are 

 quite unable to adhere to the substratum by their posterior ends 

 and so are dislodged by very slight movements of the water, 

 while the individuals with tails in the same dish hold tightly to 

 the substratum like normal animals. In such pieces the forma- 

 tion of both the postpharyngeal and the pharyngeal region is 

 completely inhibited. 



The longitudinal optical section of the different pieces shows 

 some points of interest. Figure 38 is the section of the high 

 temperature wholes, figure 39 that of the low temperature wholes 

 and figure 40 that of the tailless forms. In these last no posterior 

 elongation occurs so long as they are kept under the same con- 

 ditions, but in later stages the thickening in the posterior region 

 of the body increases and often a peculiar dorsal hump or out- 

 growth (fig. 41) appears, which contains the continuation of the 

 alimentary tract. A study of the living animals shows that 

 these dorsal elevations arise in the region where the pressure of 

 the intestinal contents is greatest when, they are forced posteriori}^ 

 and often a bulging of the body-wall is visible in this region when- 

 ever contraction occurs, even before the permanent outgrowth has 

 formed. These dorsal humps are undoubtedly the result of the 



Figures 32 to 42 Regulation at different temperatures : all pieces represent the 

 region anterior to the level 1 in the diagrammatic figure 32. Figure 33, regulation 

 at high temperature. Figure 34, regulation to 'whole' at medium temperature. 

 Figure 35, regulation to 'whole' at low temperature. Figure 36, 'tailless' form: 

 regulation at medium temperature. Figure 37, 'tailless' form: regulation at low 

 temperature. Figures 38 to 41, longitudinal optical sections of whole and tailless 

 forms. Figure 42, whole produced by subjecting a tailless form to higher tempera- 

 ture. 



