OF THE PHYTOZOA. 137 



rounded by a narrow reddish halo (figs. 1, 2, 3, 8). Dilute acids render 

 this more distinct. At the anterior extremity, close to the margin, there are 

 two reddish vesicles, the contractions of which may easily be recognized in 

 individuals in a state of repose. The hinder extremity always contains a mass 

 of granules with dark outlines, which are not altered by acetic acid. A weak 

 solution of iodine in iodide of potassium gives them a deep blue colour, gene- 

 rally verging upon black, as it is difficult to hit the right quantity of the reagent 

 to be added. The fine blue colour is better attained by the addition of dilute 

 solution of iodine in chloride of zinc, as with this the granules become shghtly 

 liquefied, and when left standing for some time even form a blue paste. Muriatic 

 and sulphuric acids also dissolve them, so that the subsequent addition of iodine 

 gives the whole body a blue colour. When the putrefaction of the infusion 

 is going on very rapidly, the granules fill the entire body. They are not 

 arranged in balls like the nutritive 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 pig- 

 ment, 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 identity 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 simultaneously in a great number of indi- 

 viduals. Certain peculiarities of their abode appear therefore to have an 

 influence upon the form. Very compressed forms are rare. However, it not 

 unfrequently happens that, whilst the investing membrane retains its normal 

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

 Sometimes it Hes 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 pos- 

 terior extremity ; in the latter case it is connected with the anterior extre- 

 mity by a slender filament (fig. 14). In infusions in which fermentation has 

 long ceased, and which contain a large quantity of brown humus -hke matter 

 but very small portions of nitrogenous substances in solution, the two last 

 modifications of the parenchyma are most frequently met mth. 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 Poli/toma 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 \dbrations upon a central point. If a movement in the opposite 

 direction is taking place, the animal is endeavouring to turn the anterior 

 extremity ; and until this is eff'ected 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 anterior 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 is stiU unintelligible 

 to me. In any case, some contrivance for this purpose, however simple, must 



