240 WM. S. MARSHALL AND C. T. VORHIES. 



other piece to make total length of shell 10 mm. Sixth, the 

 posterior end was turned, total length of shell 10.5 mm. 



8. Second, shell 9 mm. long was cut : on the following day 

 the posterior piece had been thrown off and 3 mm. added to 

 anterior end of remaining part. Fourth, posterior end had been 

 turned ; 3 mm. of the new shell removed. Fifth, 1.5 mm. added. 

 Seventh, total length of shell now 7 mm.; following day the 

 larva was dead. 



9. A shell 12 mm. long was cut and on the following day the 

 two pieces were glued together and a few new sand grains added 

 to the anterior end. 



10. A shell 12 mm. in length \vas cut and on the following 

 day the posterior part had been thrown off and 5 mm. added to 

 anterior end of remaining part. After an interval of one more 

 day 7.5 mm. of new shell had been added ; total length 12.5 mm. 



11. Fourteenth, shell 12 mm. long cut. Fifteenth, posterior 

 part had been thrown off and 2 mm. added to anterior end of 

 remaining part. Sixteenth, 5 mm. more added. Seventeenth, 

 0.5 mm. added: total length 9.5 mm. 



12. Thirty-first, case 11 mm. long was cut. First, posterior 

 part thrown off and 4.5 mm. added to anterior end of other part. 

 Second, no change. Third, cut again at boundary of old and 

 new parts. Fourth, the posterior piece again thrown off and 

 enough added to make total length of case 10 mm. Eighth, 

 posterior end turned, total length of case 10.5 mm. 



In but one of these experiments did the larva glue the two cut 

 margins together and when this had been done the case was 

 nearly as good as before cutting, except its greater flexibility 

 and a slight lack of strength. In every other experiment the 

 larvae threw off one of the pieces, always the posterior, and built 

 on to the anterior margin of the remaining (anterior) piece. The 

 construction of the new part of the case was rapid, averaging 

 nearly 4 mm. the first twenty-four hours ; to this more material 

 was added until the case had entirely or nearly reached the origi- 

 nal length. One half of the case is not long enough to entirely 

 conceal the body of the larva and the first work is to increase 

 the length of the case sufficiently to do so, after which what we 

 might call the finishing touches, i. e., turning in the posterior 

 margin and building of a hood at the anterior end are finished. 



