494 



The way in which the coil develops suggests the possibihty 

 of several sorts of anomaUes, some of which were observed in a 

 series of one hundred adults and one hundred embryos examined 

 for this purpose. Five of the adults had coils with an addi- 

 tional half- turn, just as the embryo of 180 mm. shown in figure 

 18 has half a turn more than is usual at that stage (cf. fig. 16). 

 No adult showed less than four revolutions, and none showed 

 reversals or other malformations of the spiral. Among the 

 embryos, anomalies were more abundant. Figure 21 represents 

 the colon of an embryo of 55 mm. which is placed beside a nor- 

 mal one (fig. 20) for comparison. In the anomaly the basal 

 coil has begun to rotate dorsally and to the right, in the reverse 

 direction. Three other specimens of coils reversed from the 

 base were found among the one hundred examined. A second 

 type of anomaly was observed in an embryo of 108 mm. (fig. 23, 

 likewise placed beside a normal specimen, fig. 22). Here the 

 spiral began to wind in the normal direction, but evidently 

 encountered a sharp flexure which could not be taken up, so that 

 a reversal occurs at the point x. Presumably at a stage cor- 

 responding with that shown in figure 8, such a bend as is there 

 labelled a persisted, and the advancing apex took the direction 

 of the flexure b. Accordingly, beyond the point x in figure 

 22 the coil is reversed. The inner coil has adapted itself to the 

 outer throughout, and in its concealed portion it reverses its 

 course opposite x. Another very similar anomaly was found 

 in an embryo of 95 mm., in which the inner coil likewise re- 



