as Infusoria flagellata. 251 



For the sake of accumulating and multiplying diagnostic 

 characters that shall serve us hereafter as discriminative points 

 in determining the classificatory relations of Flagellata, it is 

 most desirable that every critical study of one of these forms 

 should be carefully recorded, even to the minutest details. 

 On this account, therefore, and particularly in the present 

 connexion, notwithstanding that this species is so frequently 

 met with, and apparently so well known, it will not be out of 

 place here to describe it anew, especially as some of the fea- 

 tures presented for the consideration of natm-alists are not in 

 accordance with the interpretation put upon them by previous 

 observers. 



The body of this animalcule is colourless, but frequently has 

 a slight yellowish or reddish tinge, which is derived by diffu- 

 sion from the granular contents of the interior. The only 

 legitimate colour present lies in the very faint red eye-spot [s). 

 The form is variable, from elongate-ovate to cylindrical, with 

 a gentle taper at the anterior third into a narrow truncate- 

 emarginate head. Posteriorly the dorsal region is rounded ; 

 but on the ventral face a broad triangular prolongation (.^^), 

 already spoken of as the homologue of the guhernaclum of the 

 reptant Heteronemata, extends backward beyond the outline 

 of the dorsum. The exact relation of this prolongation to the 

 axis of the body is not to be determined beyond a doubt, be- 

 cause of the constantly shifting attitude of the animal : at one 

 moment the gubernaAiim {fi^) is on the left, and then at the 

 next instant it appears on the right of the mesial line, or fol- 

 lows for awhile between these two points, according as the 

 body keels over more or less from one side to the other or ba- 

 lances itself in a median position. It appears most frequently, 

 however, to be unilateral. 



The amoeboid contortions (fig. 46) of the body have already 

 been mentioned ; but I would add that this is only a resem- 

 blance, a mere suggestion, if one may use the term, of the 

 mode of locomotion of Amoeha ; for it is not, as in the latter, 

 an actual flowing out of a glairy mass into protean reptant 

 processes, but an exceedingly variable 'puckering^ and always 

 accompanied by a longitudinal contraction of the body, the 

 one being evidently necessary to the other. If I may carry 

 out the niceness of distinction further, I should say that, whilst 

 Amoeha is contractile and plastic, Astasia is retractile and 

 flexible. 



The flagellum {fl) also, by its subterminal attachment to 

 the head, carries out the typical plan of the reptant Hetero- 

 nemata. It is based strictly on the ventral side of the front, 

 descending from the latter with such an abrupt turn forward 



19* 



