No. 2.] SPIRAL MODIFICATION OF METAMERISM. 247 



It is not necessary that the spirals should begin in a split- 

 metamere, although this is the commonest method of procedure. 

 The greatest complexity is found in the double and triple spi- 

 rals. For instance, if the first metamere of Fig. 2 had been 

 split twice instead of only once, then it will be seen that two 

 sets of spirals will be started, twisting around the body. Or the 

 same result is obtained if a split-metamere be interpolated in a 

 spiral so as to increase the number of half-metameres on one 

 side. Lastly, if two split -metameres be interpolated, as in the 

 last case, then a triple spiral will be formed. On the ventral side 

 of the spiral the usual number of setae are present, i.e. two pairs 

 to each turn. Within the body, the nephridia follow the usual law. 

 But by far the most interesting conditions are to be found in 

 the septa. The septa follow the spiral arrangement of the meta- 

 meres. It will be seen at once that this results in a corkscrew- 

 like arrangement of the septa. That is to say, that instead of 

 a series of septa there is a single spirally winding septum, begin- 

 ning with the half-septum of the split-metatnere above and ending 

 in the same below. Or it may be said that there is a continuous 

 body cavity lying between the coils of the septum, and this 

 cavity is continuous from the top to the bottom of the spiral. 

 I cannot dwell further on this here, or discuss the variations 

 to be found in the septa. 



Let us turn now to another side of the problem. Keeping 

 capsules containing embryos of Allolobophora foetida, I was 

 enabled to examine young worms immediately on their emer- 

 gence from the cocoon. These embryos showed all the com- 

 mon forms of abnormalities to be found in the adult worms. In 

 one lot there were 120 normal embryos to 25 abnormal, or as 

 1:5. In other words, there are fewer cases of abnormalities in 

 the young worms (i to 5) than amongst the adults (i to 2). 



This apparent contradiction finds largely its explanation in 

 the fact that the adults are often found regenerating lost meta- 

 meres, and proportionally the number of abnormalities in these 

 newly formed parts is greater than in the embryos. Thus, out 

 of a lot of 525 worms, 40 were found showing regenerating 

 metameres behind. (More than this number probably had 

 regenerated metameres, for after a certain stage it is impossible 

 to distinguish the new metameres from the old.) Out of these 

 40 worms, there were 2 in which the metamerization had not yet 



