410 EVENINGS AT THE MICEOSCOPB. 



surface, "but cause the detached fragments themselves 

 to wheel round and round, and to swim away through 

 the water. Though there is not the slightest trace of 

 fibre in the structure of the acontium, when scrutinized 

 even with a power of eight hundred diameters, the 

 clear jelly, or sarcode, of which its basis is composed, 

 is endowed with a very evident contractility ; the 

 filament can contract or elongate ; can extend itself in 

 a straight line, or throw its length into spiral curves 

 and contorted coils ; can bring its margins together, or 

 separate them in various degrees ; can perform the one 

 operation in one part, and the other at another, and 

 thus can enlarge or attenuate the general diameter 

 of the cord, apparently at will ; and some of these 

 changes can be effected even in the fragment detached 

 from the animal, thus proving that the motile power, 

 whatever it is, is localized in the constituent tissue 

 itself. 



Under pressure the edges of the flattened acontium 

 appear to be thronged with clear viscous globules, 

 overlapping one another, and protruding ; indicating 

 one or more layers of superficial cells, doubtless form- 

 ing the epitheliam. As the pi-essure is increased, 

 these ooze out as long pear-shaped drops, and imme- 

 diately assume a perfectly globular form, with a high 

 refi'active power. Below these are packed a dense 

 crowd of cnidoB, arranged transversely. 



Before we proceed to the examination of these 

 curious organs in detail, it may be well to devote a 

 moment's attention to the mechanism by which the 

 acontia themselves are projected from the body. As 

 this was first described (so far as I am aware) by 



