as Infusoria flagellata. 255 



surface with scarcely a perceptible eifort, and at another pro- 

 gressing with a laborious hitching gait, and lashing its guher- 

 naclum (Jl^) about, and swinging its body from side to side, 

 with frequent jerks, in its efforts to pass over some obstacle. 



The bod^ is colomdess and enclosed in an uncontractile, 

 smooth integument. It has an asymmetrically ovate shape, 

 rounded behind, and rapidly narrowed anteriorly into an ob- 

 lique, truncate, conical front. Dorsally it is convex (figs. 67, 

 68) ; but ventrally, ^. e. on the reptant side, it is concave on the 

 right and in the middle, and so strongly incurved on the left 

 that its sharp edge (t) reaches nearly to the median line. Be- 

 neath this inrolled border the enclosed space (fig. 68, ^^) pro- 

 jects into the left side like a longitudinal covered way. In 

 front it is very deep, but from that point going backward it 

 narrows gradually, and finally, with the inrolled edge, fades 

 out at the posterior third of the body. 



The two flagella {jl^ fl'^) are as widel}^ diverse in character 

 and function as any two similar organs in the whole group of 

 Protozoa. The anterior one {fl) is, strictly speaking, the pre- 

 hensile organ, as well as the main propulsory agent. It is 

 quite delicate, and tapers gradually, from its subterminal base 

 within the longitudinal covered way, to an extremely fine tip. 

 In point of length it varies from one-half to two-thirds longer 

 than the body. It is always carried in an extended position 

 in front, and vibrates very actively, especially dm-ing repta- 

 tion. 



The posterior flagellar organ, or guhernaclum (j^*), is from 

 three to fom- times the length of the body, and arises far from 

 the front, in the deepest part of the covered way (fig. 68, t^)j 

 and immediately beneath the contractile vesicle {cv). It is 

 therefore attached quite near to the left margin of the body, 

 and between the anterior and middle thirds. Its base, which 

 is applied very obliquely to its point of attachment, is quite 

 broad ; but it narrows rapidly into a uniformly but scarcely 

 tapering lash, which always projects forward more or less, and 

 then cmwes backward and extends to a long, distance behind. 

 Dm*ing reptation over smooth sm-faces, it lies along the abdo- 

 minal median line, and trails behind in long gentle midula- 

 tions. Although it never vibrates, it frequently lashes about, 

 and applies itself against obstacles on the right and left, or 

 even in front, and acts as a prop upon which the body is 

 thrown to one side or the other, according to varying cir- 

 cumstances. That it is conti-actile would seem incontestable 

 upon observing the sudden jerk with which it sometimes draws 

 the body back toward its distal end ; but I am pretty well 

 convinced, from a careful study of this movement, that, al- 

 though this organ may be to a slight degree resilient^ it is not 



