274 Prof. H. J. Clark on the Animal Nature 



one which is globular, and then contracts suddenly and rapidly 

 until it is nearly invisible. The diastole then follows slowly, 

 aud during this it passes from a jagged rounded outline (fig. 3c?;) 

 to a lenticular form (rig. 2), then to a hemispherical shape (fig. 4) 

 with the flattened side next to the posterior end of the body, 

 and finally, assuming a spheroidal contour, it remains quiet 

 awhile, until the time for the next systole. If the water is not 

 renewed, the specimens become unhealthy, which they exhibit 

 by changing their form, and swelling up into an oval and finally 

 a globular mass. In such a condition the systole of the con- 

 tractile vesicle oftentimes occurs five or six times in a minute, 

 and will continue at that rate even when the animal is very 

 much flattened out, and until it bursts or falls to pieces. Tinc- 

 ture of opium stops the action of the contractile vesicle almost 

 immediately, even before the rest of the body is sensibly affected 

 by it. The effect is to swell the vesicle to an enormous size ; 

 and then, breaking through the posterior end of the animal, it 

 expands to a dimension often exceeding that of the whole body, 

 before it bursts. 



The Mouth (in). — That this creature has a mouth might be 

 premised from the manner in which particles of indigo or car- 

 mine approach and recede from the body. When the animal is 

 moored by its flagelliform appendage (ft), and gyrates about it 

 as if on a pivot, these particles of coloured food may be seen to 

 pass along the face of the broad longitudinal depression (d), 

 and, striking the body just behind its mid-region, glance off in 

 a backward direction. At the point where the indigo strikes 

 may be seen an obliquely longitudinal ovate opening (m), which 

 leads into an elongated funnel-shaped cavity (oe) : the former is 

 the mouth, and the latter is the oesophagus. The mouth lies 

 altogether within the posterior obliquely transverse furrow (pf), 

 and extends from its anterior to its posterior edge, trending 

 diagonally across the axial plane of the body, from the right, 

 backwards, toward the left. Its anterior edge (wt 1 ) is broad, 

 and thence it gradually narrows to a sharp angle, which forms 

 the posterior edge. It is so inconspicuous that in all probability 

 it is nearly or altogether closed, except when taking in food ; 

 certainly it is not one of the prominent features of the organism, 

 although one of the most important. When the animal is in a 

 sickly condition, and swollen up, the mouth is easily descried; 

 but its relations are not readily made out, because in this state 

 the annular furrows are all obliterated; yet its connexion with 

 the oesophagus at such a time is clearly seen. There are no 

 appendages whatever about or belonging to the mouth ; not 

 even the flagelliform body (ft) has anything to do with it, but 

 is attached to the body at a very sensible distaucc (ft) behind 



