422 ORDER FLAGELLATA-EUSTOMATA. 



sive, located at the anterior extremity immediately beneath the insertion of 

 the flagella, visible only at the time of food ingestion, not supplemented 

 by a distinct pharyngeal passage ; feeding voraciously on other flagellate 

 types, which they swallow whole. Inhabiting vegetable infusions. 



This genus is instituted for the reception of two species corresponding with one 

 another both in their broad external features and in their active predatory habits. 

 This latter characteristic, combined with the equal size of the flagella and their 

 comparative persistency of contour, serves to distinguish them from Zygoselmis, with 

 which they otherwise to a considerable extent agree. 



Dinomonas vorax, S. K. PL. XXIV. FIGS. 46-48. 



Body persistent in shape, subpyriform, widest and rounded posteriorly, 

 pointed anteriorly and slightly curved towards the ventral aspect, about two 

 and a half times as long as broad, surface smooth ; flagella slender, vibratile, 

 subequal, exceeding the body in length; oral aperture exceedingly elastic, 

 conspicuous only during the passage of food ; endoplasm finely granulate ; 

 endoplast spherical, subcentral ; contractile vesicle posteriorly located. 

 Length of body 1-1600". 



HAB. Infusions of hay in fresh and salt water. 



This species was obtained by the author at St. Heliers, Jersey, in February 1878, 

 in an infusion of hay in spring water on the eighth day of its maceration. For the 

 next three or four days it constituted the most abundantly developed type, but at the 

 end of this period it disappeared as suddenly as it came, and was not again seen in 

 the infusion. A precisely identical animalcule was found in a contemporaneously 

 prepared hay infusion in salt water on the eleventh day of its maceration, and 

 was correspondingly fugacious. The habits of this species are eminently preda- 

 tory, the greater portion of its time being spent in hunting down and devouring 

 such other flagellate forms as may happen to be present. A few of them, enclosed 

 in a glass slide with a crowd of Heteromita lens, Monas fluida, &c., were observed to 

 rush in among these smaller animalcules where they congregated in zones near the 

 margin of the glass cover, reappearing presently with a captured monad grasped by 

 its sharply pointed distal extremity. Remaining motionless for a few seconds, this 

 captured prey was gradually absorbed, a wide, elastic oral aperture, not previously 

 visible, opening and expanding to receive it, and the chase being then renewed after 

 other victims. In this manner five or six of the smaller monads were successively 

 devoured in a very short space of time, and it was consequently not long before 

 these weaker types succumbed and altogether disappeared before the aggressive 

 inroads of the new intruders. Thus was illustrated in this humblest path of organic 

 life the persistence and immutability of that law of the " survival of the fittest " now 

 recognized as regulating the distribution of the most highly developed sentient 

 beings, and upon which the welfare and stability even of nations is dependent. The 

 movements of Dinomonas vorax, when not occupied in the pleasures of the chase, at 

 which times it darts about hither and thither with great rapidity, consist of an even 

 motion in a straight line, the snout-like anterior extremity being directed obliquely 

 downwards, while the two flagella are vibrated actively in advance. In the younger 

 and smaller examples, as shown at PI. XXIV. Fig 46, the body is considerably 

 narrower, or more attenuate in proportion to its length, 



Dinomonas tuberculatus, S. K. PL. XXIV. FIGS. 43-45. 



Body irregularly ovate, somewhat variable in form, but not metabolic, 

 most usually more attenuate posteriorly, the ventral border flattened, the 



