504 



SYSTEMATIC HISTORY OF THE INFUSORIA. 



Polytoma and Chlami/domonas ; for he proposes (EntiuicJc. p. 140) to apply to 

 P. Uvella the name of Chi. hyalina. 



Genus POLYTOMA (XVIII. 5 ; XX. 1-14).— Mouth terminal, truncate, 

 surmounted by a double flagelliform filament situated as in Monas and Uvella ; 

 eye and tail wanting. It will not imbibe colouring matter. A large con- 

 tractile vesicle and the trace of a nucleus are sometimes observable. Self- 

 di\4sion occurs both transversely and longitudinally, and produces a berry-like 

 cluster of many individuals. As the young increase in size, the parent body 

 assumes a decussated or wrinkled appearance, like a mulbeny, and in this 

 manner indicates its approaching self-division into manif sections (as the name 

 Polytoma denotes), or numerous individuals. In swimming, the filaments are 

 extended in advance. In putting foi^ard the self-division of Polytoma as a 

 peculiar feature, Cohn says that Ehi-enberg has mistaken a transitional for a 

 permanent condition. It was known to Midler and Wrisberg. 



Polytoma Uvella {Monas Uva, M.). 

 — Colomless, of an oval or obloug form ; 

 extremities equally obtuse. It is often 

 abundant in water where animal matters 

 are in solution, upon which it appears to 

 be nourished ; generally in company with 

 species of Vibrio and Spirillum^ and some- 

 times with Uvella Uva and U. Atomus. 



Group 5 shows two isolated indi- 

 viduals ; another about to divide longi- 

 tudinally; a cluster of eight imited 

 within a conmion envelope ; another 

 cluster, of which the common envelope 

 has disappeared prior to the separation 

 of the individual Monads, and in the 

 two isolated beings the double filament 

 is very distmct, 1-200" to 1-90"; 

 diam. of clusters 1-380". 



Schneider (Part I. p. 136) has closely 

 examined this species (xx. 1-14). The 

 hyaline investing membrane, he says, 

 can be distinctly displayed by using 

 chromic acid, or solution of iodine in 

 chloride of zinc. A globidar nucleus 

 lies near the centre, with a narrow red- 

 dish halo around it : dilute acids render 



this more distinct (xx. 2). At the 

 anterior extremity are two reddish vesi- 

 cles, which are contractile ; and other 

 non-contractile reddish ones are scattered 

 in the interior. The creature " rotates 

 upon its axis ; and this, again, describes 

 circular vibrations upon a central point." 

 Self-division takes place at first into two 

 (xx. 3), then into fom' (xx. 9), and, under 

 favourable conditions, mto eight seg- 

 ments, each of which acquires its fila- 

 ments, and moves about within the en- 

 velope of the parent with the rest imtil 

 set free by its rupture. Under certain 

 circumstances the individuals pass to a 

 state of rest (xx. 7), and then do not 

 imdergo fission or any other change, but 

 remain in a torpid condition. In assum- 

 ing this state the filaments contract 

 gradually, and at length seem to be 

 withdra-wn completely within the con- 

 tained substance of the encysted being. 

 The internal granules of Polytoma are, 

 according to Schneider, composed of 

 starch, and are convertible into a blue 

 or a green colouring matter. 



Party has distinguished three additional species, viz.- 



POLYTOMA 



many as ten 



Uva. — Divides into as 

 segments. The mode of 

 fission much resembles that of Chlamy- 

 domonas, but differs in exhibiting active 

 movements during the process, instead of 

 the state of rest seen in the latter. The 

 corpuscles are usually oval, and hya- 

 line ; rarely yellow or brown ; filled "u^th 

 larger or smaller vesicles, and in old 

 specimens with black molecides. Self- 

 di\ision proceeds rapidly. Movements 

 darting and revolving. An enveloping 

 cyst has been noticed in some examples. 

 Uncommon in fresh, but frequent in 

 water holding animal decomposing mat- 

 ters in solution. Two varieties are 



distinguishable: viz. — Var. a uni/iliSf 

 having only one filament, resembling 

 Trachelim ghhulifer (E.), and very pro- 

 bably identical with Monas puncfimi; 

 Var. b. 7'ost7'ata seu hysginoides, of a 

 feeble yeUow colour, with a prominent 

 cyst-wall, within which it is contracted 

 and deprived of its filaments. It does 

 not break up on drying, but can continue 

 several weeks without change. [This is 

 evidently not even a variety in the proper 

 sense, but simply an encysted Polytoma.'] 

 P. ocellata.—OYB\', filled with vesi- 

 cles, like P. Uva, except that it has a 

 clear-red stigma at the centre. Motion 

 languid. Self-fission produces few new 



