126 H - JAMES-CLARK ON THE ANATOMY 



posterior borders. Its surface is beset with excessively minute, short cilia, which, although 

 occasionally and with great difficulty seen to move, cannot be called vibratile cilia in a 

 strict sense, but rather pointed roughenings which are agitated by the varied contractions 

 and expansions of the tissue from which they arise. The thickness of this wall is more 

 or less deeply corrugated, principally in a longitudinal direction (fig. 14, r, r), and to a 

 certain extent independently of the irregular folds and furrows on the outer surface of the 

 inner wall. 1 



§ 7. The Circulatory System. 



It would seem a little remarkable, at first thought, that the Vorticellidie, which hold the 

 highest rank among Infusoria, should possess a circulatory system Avhich, in all but one 

 genus, seems as simple in character as that of the lowest forms of the class, and apparently 

 much less complicated than in Sicnior and Paramecium, and others of the lipotropic division. 

 If, however, we look upon the numerous contractile vesicles of Ampldhptus, Trachelitis, etc., 

 as indications of a diffuse, lowly organized circulatory system, and upon the fewer 

 branching vesicles of Paramecium, Spirostomum, Stentor, etc., as tendencies to a greater 

 degree of concentration, then the unique contractile organ of Vorticellidans would represent 

 the consummation of this process, and consequently the most elevated status of the system, 

 as it exists in this class of animals. 



The contractile vesicle (cv) of Trichodina is a simple cavity which lies near the ventral side 

 (figs. 8, 11) of the animal, a little to the left of the axial plane (figs. 12, 13), and conse 

 quently on the same side of the oesophagus, and about half-way between the anterior and 

 posterior truncate ends of the body. 2 It contracts once in fifteen seconds. The systole 

 occupies 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 max- 

 imum size (figs. 8, 11, 13, 14), and then it immediately contracts again. In specimens 

 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. The Reproductive System. 



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 l ) 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 

 (m 1 ) lay next the ventral side, and right and left of the plane which passes through the 

 oesophagus ; and its breadth ran parallel with the axis of the body. It had a decidedly 



1 See, for further details, the section (§ 3) on the funn. anterior end of the body, bat the latter is posited as ifseenfrom 

 of the body. the front. To correct it, the contractile vesicle should lie to 



2 There is a singular error in Stein's figure (Infusions- the right of the oesophagus, and the sigmoid flexure of the 

 thiere, 18.34, taf. VI. fig. 56) of the animal as seen from the vestibule and oesophagus should be reversed. 



basal end. The view of the base is underlaid by a view of the 



