242 \VM. S. MARSHALL AND C. T. VORHIES. 



hard one is evinced by the fact that we have, during our experi- 

 ments, found larvae which have been " stuck " in turning and 

 died without being able to completely turn. 



NOTCHES CUT AT THE POSTERIOR END. 



i. Four cases were cut, two dorsal and two ventral. The 

 two ventrally and one dorsally notched case were closed the fol- 

 lowing day, but without the use of sand, the secretion from the 

 spinning glands being used and the cut edges partly drawn 

 together. The fourth specimen did nothing on the first two 

 days ; the third day, and, thereafter each day for five days, new 

 grains were added to the anterior end until a new part 4 mm. in 

 length had been built. 



Two experiments were made by cutting, day after day, a small 

 piece from the posterior end of the case, thus forcing the larva 

 to add continually to its case if it desired to keep it long enough 

 for its body. It was found that either daily or every two or 

 three days a small portion would be added ; if daily, a smaller 

 amount than if the larva waited one or two days before making 

 the repair. No tendency to exhaustion of the silk was notice- 

 able during the three weeks or more that the experiments lasted. 



No. i built a total length of new case 17.5 mm. in twenty-one 

 clays ; average 0.83 mm. daily. 



No. 2 built a total length of 19.5 mm. in twenty-three days ; 

 average 0.84 mm. daily. 



With several larvae the experiment was tried of driving them 

 out of their cases and then placing both larva and case in the 

 same dish to ascertain if they would return to old case. Two 

 larvae were placed in each dish, a large and a small one, to see 

 whether a larva would occupy a case built by another ; with this 

 arrangement there could of course be but one change, that of 

 the smaller larva into the case of the larger. When new cases 

 were constructed these were destroyed leaving only the original 

 ones. 



I. Did not return to old case. Built a total length of 32 mm. 

 of new case in the first four days. Rested a day and then added 

 6 mm. more in two following days. Total length of new case 

 built in seven days 38 mm. Average 5.42 mm. per day. 



