302 ORDER FLAGELLATA-PANTOSTOMATA. 



contractile vesicles, demonstrates the entire compliance of these organisms with the 

 formula adopted at the commencement of this work for the distinction of all typical 

 Infusoria. 



Polytoma uvella, Ehr. PL. XV. FIGS. 67-78. 



Body ovate or oblong, equally rounded at the two extremities, or 

 slightly more pointed at the anterior one, invested by a delicate hyaline 

 membranous cuticle ; flagella inserted close to one another at the anterior 

 extremity, of equal size, exceeding the body in length, having apparently a 

 small bead-like or fusiform inflation at their point of origin, such ap- 

 pearance being produced by a minute loop-like basal flexure ; this basal 

 region of the flagella, soft and adhesive, enabling the animalcules to 

 attach themselves at will to foreign objects ; contractije vesicles two in 

 number, anteriorly situated ; endoplast central, spherical ; endoplasm of the 

 posterior half of the body usually more coarsely granulate. Length of body 

 1-1200" to i -800". 



HAB. Fish and other animal macerations. 



In describing the form, as quoted overleaf, under the title of " the biflagellate or 

 acorn-monad," Messrs. Dallinger and Drysdale appear to have been unaware of its 

 identity with the Polytoma uvella of Ehrenberg, and of the results of Schneider's and 

 Perty's investigations. These last-named authorities, while by no means supplying 

 a complete and exhaustive account of its reproductive history, assist materially 

 in the interpretation of certain phenomena, which have been left unexplained by 

 our fellow countrymen. As first made known by Schneider, and since shown by 

 Messrs. Dallinger and Drysdale, the animalcules increase rapidly by a process of 

 multiple fission, caused by the first dividing into two, and then into four, eight, or 

 even sixteen segment-masses of the entire protoplasmic mass enclosed within the 

 external hyaline cuticular membrane, and quite independently of that structure. 

 These divided portions assume the shape and aspect of the parent monad, the flagella 

 often perforating and protruding through the cuticle of the latter, as shown at 

 PI. XV. Fig. 73. The organism now swims about with its contained young for a 

 longer or less duration of time as an apparently compound organism. It was 

 this pseudo-compound phase, indeed, that Ehrenberg regarded as the normal one, 

 and upon which he conferred its characteristic title of Polytoma. Subsequently, each 

 of these subdivided portions breaking through the investing membrane of the parent 

 monad, assumes an independent existence, leaving the latter as an empty and 

 lifeless cyst While the products of this multiple fission process may continue 

 increasing in a similar manner for many generations and without the intervention of 

 the coalescence or genetic union of two zooids, it has been shown by Messrs. 

 Dallinger and Drysdale that there is yet another mode by which the perpetuation of 

 the species is asexually accomplished. In certain examples under examination it was 

 observed by these authorities that the posterior portion of the body was almost filled 

 with granular masses of protoplasm, which conveyed to this region a roughened 

 acorn-cup-like aspect as compared with the smooth and hyaline anterior portion ; 

 carefully watching them it was found that in the midst of their swiftly moving course 

 these acorn-like zooids would suddenly discharge the entire contents of the posterior 

 region as separate granular fragments into the surrounding water, as shown at 

 Fig. 75. Each of these fragments thus liberated was amorphous in form, more or 

 less agglomerated and perfectly transparent. Examined attentively with the aid of a 

 magnification of 2500 diameters and upwards, minute dots were next seen to 

 make their appearance in these granules, which increasing in size, exhibited active 

 vibratory movements and were ultimately released as minute bacterium-like bodies. 

 The growth of these liberated particles within a space of four or five hours to 

 monads identical in size and structure with the parent form, was subsequently 



