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at successive depths caused a migration of the worms deeper and 

 deeper into the mass, where moisture was still present. A number 

 of tests were made to determine how long these worms could live 

 when removed from water or wet sludge and transferred to a dry 

 place. The specimens were cleaned and tested singly. There was 

 some variation, but in general the time was limited to 3 to 5 minutes 

 when the experiment was carried on under the conditions which ex- 

 ist at the Testing Laljoratory. Beyond this time the worms failed to 

 revive when returned to moist conditions. A mass of the worms, 

 composed of a number of individuals, had a much higher resistance 

 than a single worm. 



THIGMOTACTIC RESPONSE 



These lumbricillid worms exhibit a considerable degree of positive 

 thig-motaxis. This is shown by the frequency with which numbers 

 of them are seen under natural conditions to progress in aggregations 

 side by side. They are also often found grouped together in masses 

 on the surfaces of the filter-bed rock. When a large number of speci- 

 mens are transferred to a watch-glass containing tap water they show 

 a distinct tendency to mass themselves around any solid particle or 

 small mass of sludge which may have been transferred with them. 

 This often proved to be of advantage in the putrescibility tests, since 

 the transfers from the different containers could be easily made by 

 picking up the whole mass of one hundred worms at once. The ten- 

 dency to accumulate in masses seems to be accentuated when the 

 worms are placed under slightly unusual conditions. In case these 

 masses are left undisturbed for a time the worms often ultimately 

 begin to disperse in a rather characteristic manner, moving on the 

 supporting surface in several separate aggregations, the individuals of 

 each lying compactly side by side and all moving in the same direc- 

 tion. Specimens were frequently placed in temporary storage in Syra- 

 cuse watch-glasses containing a small quantity of water and each 

 one covered by another watch-glass. After these glasses had stood 

 for some time the worms almost invariably accumulated all around the 

 upper rim of the lower watch-glass at the point where the upper glass 

 touched the lower. They apparently preferred a position where they 

 secured the maximum contact with the glass. Specimens kept in Petri 

 dishes commonly accumulated between the perpendicular sides of the 

 upper and lower dish ; and those kept in dishes containing wet filter 

 paper usually sought positions between the filter paper and the sides 

 or bottom of the dish. 



