Physiology of Trichodina pediculus. 419 
between two and three seconds, and the diastole proceeds slowly 
and continuously during the remainder of the quarter of a 
minute, until the vesicle has attained its maximum size (figs. 8, 
11, 13, 14), and then it immediately contracts again. In speci- 
mens which are confined, or in the least restrained in their 
movements, the systole and diastole succeed each other much 
less frequently. At the full diastole the vesicle is perfectly 
globular, and occupies at least one-third of the diameter of the 
mid region of a fully expanded animal. The systole reduces it 
to an almost invisible point ; and from this it gradually expands, 
first into a jagged (fig. 10, cv) star-like cavity, then into an 
irregular spheroid (fig. 12), and finally assumes, at full diastole, 
a globular contour. 
§ 8. Tur Rupropuctive Sysrem.—As these observations 
extend over but a few days (mostly at the beginning of October 
of this year), the different phases in the development of the 
nucleus were not investigated. At the period just mentioned, 
this organ (n,n!) had the form of a thick, knotted, or monili- 
form band, which extended in a uniform curve, over three- 
quarters of a circle, around the truncate base, and in a direction 
exactly transverse to the axis of the body. Its two ends (n!) 
lay next the ventral side, and right and left of the plane which 
passes through the cesophagus; and its breadth ran parallel 
with the axis of the body. It had a decidedly yellow colour, 
and was finely granulated throughout. In profile, or rather m 
a foreshortened view of its length, it was quite conspicuous ; 
but where it extended across the vision, it was so excessively 
faint as to nearly escape the eye, even though the utmost care 
was taken to ascertain its presence and exact position. 
§ 9. Resume*.—Reducing, now, the details which have been 
given in this memoir to the briefest expressions, we have the 
following summary in an aphoristic form. In its healthy, un- 
restrained condition, Zrichodina pediculus is very dissimilar to 
the hitherto published representations of it. The illustrations 
of Ehrenberg, Dujardin, Stein, and Busch represent the animal 
in an abnormal, more or less reverted attitude, the result of 
studying the animal in a confined state, or when in an un- 
healthy condition. It has a deep, cyathiform, or dice-box shape, 
with an irregularly and longitudinally furrowed and plicated 
exterior. There is no disk, or it is represented by the depressed 
cupuliform area which is bordered by the vibratory crown. The 
peristome is not a closed circle, as in Vorticellidee proper, but 
* The principal points of this résumé are to be found in the ‘ Proceedings 
of the Boston Society of Natural History,’ Oct. 18, 1865. 
a7t 
