32 



G. 0. SARS. 



[NO, 1. 



m: 



Physiology. 



A. Motion. 



a. The Locomotion. 



The locomotion of the animal is foimd to be of two rathei 

 different kinds. In the one case, it is accomplished when the animal 

 is freely suspended in the water: in the other, it takes place 

 while it dwells on the bottom; in the former case, it is a swini- 

 ining motion; in the latter, a creeping, or more generally a burro Yv- 

 ing, motion. The means by which these two kinds of locomotior 

 are effected, are also rather different. 



The swimming motion is performed exclusively by the aid 

 of the antennæ, the repeated strokes of which propel the animal 

 through the water. During this motion, the said organs, togethei 

 with the anterior part of the head, remain exserted from the 

 front part of the shell, being moved laterally to a greater or less 

 extent (see Pl. I, fig. 3, Pl. III, fig. 1). The locomotion effectec 

 by this means, is not very rapid, nor abrupt or jerking, but a 

 perfectly even run through the water, whereby the animal as a 

 rule turns the dorsal part up. Not rarely, however, this attitude 

 becomes changed, and the animal is often observed to revolve 

 several times before breaking off the motion and sinking to the 

 bottom. On the whole, the SYvimming motion Yvould seem to be 

 effected Yvith considerable effort, especially when the specimem 

 are loaden with young brood; and hence this motion is nevei 



