234 CONTRIBUTIONS TO THE NATURAL HISTORY 



is in studying in tliis way all the tissues without destroying them by any pressure, it 

 must be obvious that their special character can, under no circumstances, be better stud- 

 ied than when the tissues preserve the natural turgescence of life. Of course, such in- 

 vestigations cannot be traced otherwise than by the sea-side, with all conveniences for 

 sedentary study. 



The form of Sarsia mirabilis is very peculiar, and remarkably well adapted for its rap- 

 id movements. (Plate IV.) It is somewhat bell-shaped, hemispherical; with the upper 

 vault broad and flat, and the sides rather prolonged, sometimes even in the relaxed state 

 assuming a somewhat cylindrical form, which, when more contracted, gives the whole 

 mass an almost hemispherical shape, which may, at times, really assume the appearance 

 of -a nearly globular body. And all these forms pass so rapidly from one into another, 

 that it is exceedingly difficult to say which is the more natural. I have watched these 

 animals, when they seemed to rest motionless in the midst of the waters (Fig. 1) ; they 

 then had the most regular hemispherical form ; the four arms, which then hung loosely 

 downwards, would, from the base, stretch at right angles with the lower margin of the 

 animal for a short distance, and then hang vertically downwards, for perhaps two or three 

 times the length of the greatest diameter of the central mass. After remaining for a 

 while immovable in that position, the walls of the body would relax, the arms elongate, 

 the sides hang loosely downwards, and the whole body assume a more cylindrical form, 

 when the arms hang straight downwards in graceful undulations, and without forming 

 any marked angle with the base of the animal. (Fig. 10.) In this state of relaxation, 

 the tentacles would elongate for three, four, and even more than five times the length of 

 the greatest diameter of the animal ; but if, suddenly starting from this inactive position, 

 it contracts powerfully to move onwards, in its first contraction, or for several contractions 

 repeated in quick succession, it assumes an almost entirely spherical form (Fig. 9), the 

 thinner margins contracting more extensively than the main mass, and shutting almost en- 

 tirely the lower opening of the body, the arms following in their undulation these quick 

 contractions, which press the water out of the main cavity with such force as to push 

 forwards in an opposite direction the whole body, which thus advances rapidly under the 

 repeated contractions. After each contraction, and during the onward movement arising 

 from it, the tentacles point directly backwards. During each contraction they are con- 

 siderably shortened, and elongate gradually in the progress of locomotion. (Fig. 8, 11, 12.) 

 This animal seems very well to understand how to direct its course by its contractions, 

 as it will dart downwards, if it be near the surface of the water when started, or it will 

 move sideways if it be near the walls of the jar, or it will rise upwards if it be at its 

 bottom ; it will suddenly change its direction if it meets an obstacle, turn once or twice 



