Use of SVime -threads in the Marine MuUusca. 357 



Eolis drummondi, Tliompsoii. — One of several fine speci- 

 nieiis fully 1 inch long', dredo-ed at Skerries, was transferred 

 to a phial c£ sea-water on tlie 2J:th of July last. This was 

 an extremely lively animal, its tentacles and numerous 

 slender papillas being in perpetual serpentine motion. 

 Mounting rapidly to the water surface, it floated there foot 

 upward until a gentle tap of the phial disengaged it and left 

 it suspended from its slime-thread 2 inches below the surface. 

 With what must have been a strenuous muscular effort the 

 animal, while thus suspended by the tip of its slender tail, 

 bi ought its head, or, rather, the fore front of its foot, again 

 and again into contact with the slender suspensory thread, 

 and vigorously working its tentacles and bristling papilla in 

 such a way as to render exact observation of its climbing 

 method impracticable, it regained the water surface and 

 resumed its floating position there in the space of one minute. 

 Though the precise method of climbing was not perceptible, 

 the ascent was clearly effected along and by means of the 

 thread and by the application to it of the fore part of the 

 animal's foot. 



Skenea planorbis (Fabricius). — This diminutive species 

 appears to be peculiarly addicted to the use of the suspensory 

 thread both f(^r descending from and ascending to the water 

 surface, and though its absolute rate of progression is slow, 

 yet in comparison with the size of the animal it is quite rapid. 

 Skenea climbs by its thread fully four times its own lengtli in 

 one minute, while the much more swiftly moving EoUs 

 drummondi accomplishes only twice its own length in the 

 same time. Many specimens of khenea collected at Bullock 

 were placed under observation on the 19th April last, and 

 several of these were seen to mount by their suspensory 

 threads, the quickest rate of climbing being half an inch in 

 two minutes, while the average of a number of such climbs 

 by different individuals was found to be 1 inch in six minutes. 



As with all the other species observed, the foot and tentacles 

 of Skenea were in constant vigorous motion while the animal 

 mounted by its thread to tlie water surface. Again and 

 again one or other of the many floating individuals was seen 

 to lower itself by its thread for 2| inches. On one occasion 

 an individual having lowered itself by a series of jerky drops 

 almost to the bottom of the tube, remounted one-eighth of an 

 inch along its thread befure it finally resumed its descent and 

 r^:ached tlie bottom ; another, having descended in the same 

 manner, remounted its thread for half an inch, or, say, for 

 eight times its own length. 



