as a Craspedote Flagellate Infusorian. 79 



from each other, but always close to the periphery. These 

 clear areas are the contractile vesicles [v). They do not occupy 

 any particular place in the body, although usually they are not 

 in front. The systole and diastole are extremely slow, but 

 very distinct, if sufficient patience is summoned to watch them 

 fixedly and without interruption. The last third of the systole 

 is abrupt ; and then only does the vesicle appear to contract sud- 

 denly ; whereas by watching it through a complete circuit of 

 diastole and systole, one learns that its function is, on the whole, 

 performed very slowly. This very abrupt movement, quite 

 happily, may serve to rebut any such objection as that the 

 otherwise tardy action is merely the result of ^protoplasmic con- 

 traction of the body as in certain palmellate zoospores. Their 

 immovable position, as regards the body-contents, is another 

 item of rebutting evidence. 



The sjncula (fig. 1, e e') are very slender, slightly curved, 

 needle-shaped bodies, gradually tapering to a sharp point at 

 each end. They have a bright amber colour, and a rather dark, 

 strongly refractive outline. From tip to tip they are slightly 

 roughened by irregularly scattered, low, but acute prominences 

 or knobs. There are two kinds of spicules, large and small ; 

 but they differ in no other respect. The larger (e) are from 

 four to six times as long and thick as the smaller ones ; 

 they occur in bundles of two, three, or four, and act as props 

 to hold up the outer investing membrane, as described in the 

 early part of this article. They seldom arise perpendicularly 

 from the monadigerous mass, but more or less obliquely, and, 

 in forming bundles, stand across each other like stacked arms. 

 We seldom found spicules penetrating the monadigerous mass 

 far beyond the epithelioid inner investing membrane. They 

 evidently belong, universally, to the investing membrane, and 

 assist it in forming a framework in which the inner mass is 

 suspended. The smaller spicules (e^) are strictly confined to 

 the outer division {a) of the investing membrane, and lie there 

 on their sides, completely immersed in its thickness. They are 

 scattered irregularly and sparsely about, and frequently cross 

 each other at varying angles. We observe no nearer approach 

 to a methodical aiTangement among either the large or the 

 small spicules ; yet their veiy irregularity, being after a kind, 

 and constant in that kind, may be recognized in some sense as 

 methodical. 



General Considerations. — Seeing the secluded position of the 

 monad cephalids, deeply ensconced in little chambers below the 

 general surface of the circulatory apartment, it is not directly 

 evident that their Jlag el la have any agency in keeping up the 

 inflow and outflow of currents through the afferent and efferent 



