Natural History of the Infusoria. 323 



matter in the bodies of other Infusoria, and it is by no means 

 probable that they are taken in from the exterior. Besides the 

 two contractile vesicles, single, non-contractile, reddish vacuoles 

 are seen scattered through the substance of the body. 



The starch-like granules are often converted into an indigo- 

 blue pigment, which is then partially dissolved, and colours the 

 whole parenchyma. Such specimens as these still retain the 

 power of division, so that there can be no doubt as to their iden- 

 tity with Polytoma Uvella. Individuals were also frequently met 

 with of which the substance of the body was of a uniform 

 green colour, but which in other respects agreed exactly with 

 Polytoma. 



Deviations from this normal form never occur singly in 

 the same vessel, but always make their appearance simulta- 

 neously in a great number of individuals. Certain peculiarities 

 of their abode appear therefore to have an influence upon the form. 

 Very compressed forms are rare. However, it not unfrequentlv 

 happens that whilst the investing membrane retains its normal 

 form, the substance of the body is not equally distributed in its 

 interior. Sometimes it lies to one side, so as to fill only half 

 the interior of the sac ; sometimes it is entirely collected in the 

 anterior, and sometimes in the posterior extremity; in the latter 

 case it is connected with the anterior extremity by a slender fila- 

 ment (figs. 13 & 14). In infusions in which fermentation has 

 long ceased, and which contain a large quantity of brown 

 humus-like matter, but very small portions of nitrogenous sub- 

 stances in solution, the two last modifications of the parenchyma 

 are most frequently met with. At the same time the starch-like 

 granules disappear, the substance of the body acquires a darker, 

 fatty outline, and finally disappears, with formation of the well- 

 known large vacuoles. 



The movements of Polytoma are the same as those usually 

 ascribed to organisms furnished with two filaments. Whilst in 

 motion the filaments are always in front, the animal rotates upon 

 its axis, and this again describes circular vibrations upon a cen- 

 tral point. If a movement in the opposite direction is taking 

 place, the animal is endeavouring to turn the anterior extremity, 

 and until this is effected, it swims backwards. When a drop of 

 the infusion has been left for a few minutes upon a glass plate 

 covered over with a piece of thin glass, a considerable number of 

 the animals will be found attached to both glasses by their ante- 

 rior extremity ; the filaments are free, and it is probably by their 

 vibration that the hinder extremity is made to oscillate in the 

 direction of the plane of the two filaments. They collect in the 

 same manner in crowds upon aquatic plants, as well as upon the 

 sides of the vessel containing them. Their mode of attachment 



21* 



