GENUS MONAS. 233 



simply varieties of the same type, transitional or larval conditions of other Flagellate 

 Infusoria or Radiolaria, which commence their existence as similar simple uni- 

 fligellate beings, or it may be the initial or zoospore phases of Algae, Palmellaceae, 

 or other Protophytic plants. Such being granted, it is only in a provisional sense, 

 and until their correct status shall have been decided by the light of more modern 

 investigation, that the majority of the specific forms collated under the present 

 generic title are admitted to this volume. Of those four or five types alone that are 

 placed first on the list can it be said that sufficient is known to permit of their recog- 

 nition as distinct and independent beings, and it is upon these few only that the 

 amended diagnosis of the genus, as here given, is constructed. While thus obliged 

 to leave a considerable number of species in an undecided and probational position, 

 the main object aimed at by the author will, it is hoped, be accomplished, and the 

 genus Monas be established upon a secure and substantial footing. 



By the earlier writers, every animalcule whose dimensions were so minute that it 

 presented under the highest magnifying powers then available the aspect of a mere 

 motile speck, was consigned to this genus, while by even the most recent investigators 

 an almost equally incongruous assemblage of microscopic beings is similarly dealt with. 

 Thus Cienkowski, in his recent accounts of monadiform organisms, includes under this 

 same generic title both uniflagellate and biflagellate animalcules ; Stein, again, in his 

 recently published volume of plates, without detailed descriptions, of the Infusoria- 

 Flagellata, delineates as typical representatives of the genus Monas those triflagellate, 

 voluntarily attached, or free-swimming forms out of which, upon ample grounds, 

 Cienkowski formulated some years previously the genus Spumella. Typical members 

 of the present genus, as here defined, are in the same work referred by Stein to 

 the genus Cercomonas ; a step in the right direction being at the same time accom- 

 plished by his elimination of the stomatode forms Monas grandis, M. semen, and 

 M. ochracea of Ehrenberg, and creation for the same of the independent genera 

 Ccelomonas, Raphidomonas^ and Chrysomonas. 



Particular and accurate attention should, above all things, be directed, in the 

 future investigation of these minute beings, to the manner in which food-matter is 

 ingested, it being only those entirely free-swimming, uniflagellate forms which aie 

 capable of incepting such pabulum at all parts of their periphery, after the manner 

 of an Amaba, or which, as is probably the case of Monas Dallingeri, absorb 

 nutriment in a fluid form through the same generally diffused area, that can rightly 

 lay claim to the present generic title. 



Monas Dallingeri, S. K. PL. XIII. FIGS. 1-9. 



Body ovate, rounded posteriorly, the anterior extremity more pointed 

 and slightly curved, surface smooth ; flagellum from one to one and a half 

 times the length of the body, flexible throughout when young, rigid towards 

 the base in older specimens ; no endoplast or contractile vesicle as yet 

 detected. Locomotion straight and uniform, without jerking or irregularity. 

 Length 1-4500" to 1-4000". 



HAB. Fish macerations. 



The author has much pleasure in connecting with this species the name of the 

 authority who, in conjunction with Dr. J. Drysdale, has contributed so largely to our 

 knowledge of the minute organisms now under consideration. In their published 

 ' Researches into the Life-history of the Monads,' already quoted at pages 29 

 and 133, this particular form is figured and described * under the title of the simple 

 " uniflagellate " or " multiple-fission " monad, and was obtained in great abundance 

 in a maceration of cod's head three months old. Its life-cycle, as worked out by 

 these indefatigable investigators, yields to none in the interest and completeness of 



* 'Monthly Microscopical Journal,' vol. xi., No. Ixii., 1874. 



