GENUS PHYSOMONAS. 263 



The representatives of the Dendromonadidae present collectively a type of modifi- 

 cation closely analogous to that which obtains among the more highly organized 

 Peritrichous family group of the Vorticellidae. Here as there, while some few are 

 distinguished by their solitary habits, the large majority are conspicuous for the 

 extensive tree-like colony-stocks produced by their associated numbers. These, 

 indeed, frequently present in miniature so striking a resemblance to the tree-like 

 colony-stocks of Epistylis and other compound Vorticellidae that, in the absence 

 of magnifying power sufficient for the demonstration of their true nature, they 

 have frequently been described as diminutive forms or earlier growths of such 

 higher Ciliata. The probable derivation of the more complex dendritic forms, such 

 as Anthophysa and Dendromonas, from such a primary solitary type as Physomonas, 

 and through such a simply aggregated stock-form as Cladonema, can scarcely be 

 doubted, the fundamental contour and structure of the individual animalcules, 

 as manifested by the oblique lip-like anterior border and flagella of diverse lengths, 

 throughout this natural family group being identical. 



GENUS I. PHYSOMONAS, S. K. 

 (Greek, physa, bladder ; monas.) 



Animalcules solitary, occasionally free-swimming, but normally attached 

 by a slender, flexible, posteriorly developed, thread-like pedicle ; body sub- 

 spheroidal, anterior border obliquely truncate, provided with a projecting 

 lip-like prominence ; flagella two in number, unequal, one long and one 

 short ; endoplast and one or more contractile vesicles mostly conspicuous ; 

 no distinct oral aperture, food being incepted at all parts of the periphery. 

 Inhabiting fresh or salt water. Increasing by longitudinal fission and by 

 the subdivision of the entire body into spores. 



Physomonas socialis, S. K. PL. XIV. FIGS. 37-45. 



Body subglobose, transparent and slightly granular, obliquely truncate 

 anteriorly ; primary flagellum two or three times the length of the body, 

 secondary one less than one-half the length of the primary one ; pedicle 

 slender and flexible, equalling in length the larger flagellum ; contractile 

 vesicles largely developed, two in number, contracting and expanding alter- 

 nately, located side by side a little behind the median line ; endoplast 

 spherical, subcentral. Diameter of body 1-5000" to 1-2500". 



HAB. Pond water with decaying vegetable matter. Increasing by 

 longitudinal fission, and by encystment and the breaking up of the body 

 into spores. 



It was originally suspected that this species was either a mere variety QiSpumella 

 guttula, having but one short secondary flagellum, or that the last-named type 

 represented the present form immediately antecedent to the process of fission, and 

 when the development of supplementary flagella gives the earliest indication of the 

 approaching change. It has, however, been met with by the author on so many 

 occasions, and is found to exhibit persistently such important and fundamental 

 differences with relation to both its structural and reproductive features, as to 

 necessitate its recognition as both a distinct specific and generic form. Such 

 structural differences are conspicuously manifested, in addition to the character 

 furnished by the flagella, in the less perfectly spheroidal or globose condition of the 

 body, and in its possession of two largely developed contractile vesicles in place of 

 the single one characteristic of 6". guttula ; there is, further, no trace of the linear 



