18 C. M. CHILD 



animals, consequently the amount of coelomic fluid formed may 

 be relatively greater and the larvae therefore more distended 

 than the normal. In the differential inhibition of the sea urchin 

 one result may be over-development of the skeleton, because the 

 mesenchyme cells are the least susceptible and therefore least 

 inhibited cells of the larva, and, in differentially inhibited in- 

 dividuals, are able to obtain more than their normal share of 

 nutritive material and to increase in numbers and to produce 

 skeletal substance greatly in excess of the normal (Child '16 c, 

 p. 91). It seems probable that these distended polychete 

 larvae, like the plutei with skeletal over-development, result 

 from a differential alteration by the inhibiting agent of the 

 normal metabolic relations between different parts of the body. 



Figures 18 and 19 show three-day larval forms resulting from 

 exposure to KNC ??z/ 10000 for eleven hours, beginning forty- 

 five minutes after fertihzation. In these cases there is of course 

 more or less recovery, but here as in the sea-urchin, the differential 

 inhibiting action of KNC is remarkably persistent. In these 

 cases the head is markedly inhibited, the first larval segment is 

 overdeveloped, at least as regards size and, to a lesser degree, 

 the second also, while the third segment and the posterior growing 

 region are present merely as a more slender posterior prolonga- 

 tion (fig. 18) or in cases with a slightly greater degree of recovery 

 as a distinct region (fig. 19). The posterior terminal appendage 

 is almost completely (fig. 18) or completely (fig. 19) absent. 

 In these cases the metabolic activity of the head-region and, 

 secondarily, of the posterior growing region has undergone a 

 relatively greater decrease than that of the first and second 

 larval segments, and these therefore show a relative increase in 

 size. Incidentally it may be noted that the peculiar proportions 

 of these larvae, appear relatively late. At two days they are 

 much like those of figures 15 and 16 though somewhat larger, 

 but on the third day the regional differences become more marked. 

 The distended forms resembling figure 17, but somewhat more 

 elongated, also occur frequently and-in all degrees in these series. 



The differential results obtained with HCl do not differ in 

 any essential way from those with KNC. Much higher con- 



