POLYGASTRICA. 



Fig. 17. 



microscope, are exceedingly vivacious ; and although many of them 

 inhabit a space not larger than the point of a needle, they swim 

 about with great activity, avoiding each other as they pass in their 

 rapid dance, and evidently directing their motions with wonderful 

 precision and accuracy. Our next enquiry therefore must be con- 

 cerning the organs of locomotion which they possess. These are 

 of various kinds, and are arranged differently in different species. 

 In the smallest animalcules, monads, &c. no locomotive organs 

 have been satisfactorily detected ; yet even in some of these 

 Mons. F. Dujardin perceived one or more filaments of extreme 

 tenuity attached to their globular bodies, which he regards as 

 instruments for progression. These filaments he describes as not 

 exceeding -30 j 00 of a millimetre in diameter, and consequently 

 requiring the utmost penetration of the microscope for their detec- 

 tion. Tn Amteba diffluens (Jig. 16, #) organs of locomotion are 

 formed at the pleasure of the animal, by shooting out processes 

 from different parts of its semifluid substance, which may be used 

 as fins or legs, as occasion requires. Some are provided with styli^ 

 or articulated, stiff, bristle-like organs, which are moveable, and 

 perform in some measure the 

 office of feet, and with uncini, 

 or little hooks, serving for at- 

 tachment to foreign bodies ; 

 these are seen in Eupltea 

 Charon (Jig. 17, 4). 



(76.) But the most impor- 

 tant locomotive agents are the 

 cilia,* with which the Poly- 

 gastrica are generally fur- 

 nished (fig. 17; 1, 2, 3). 

 On attentively examining most 

 forms of these creatures, espe- 

 cially those of comparatively 

 large size, the body will be 

 seen in some cases to be en- 

 tirely covered with minute 

 vibrating hairs, or at least 

 furnished with such appen- 

 dages on some part of its surface. The existence of these cilia 

 is readily detected by a practised eye, even when using glasses 



* Cilium, an eye-lash. 



