H. JAMES-CLARK ON THE AFFINITIES OF SPONGES. 335 



that it was not possible to decide positively whether it made its exit upon the dorsal or the 

 ventral side. 



The contractile vesicle (cv) is a comparatively large organ, with a rounded contour when in 

 full diastole, and quite faint and inconspicuous. It lies above the base of the gulernaclum 

 (J 2 ), the expanded base of the latter appearing at times to form a part of it, and by its 

 movements — causing an alternation in light and shade — tends to mislead one into the 

 belief that the systole is very irregular. A careful adjustment of the lens, however, reveals 

 the true pulsation, and shows that the systole has a very slow rate. 



§ 14. Heteromastix, Jas.-Clk. 1 (H. proteiformis, Jas.-Clk.) 

 (Plate X., figs. 70, 71, 72, 73, 74.) 



I shall not describe this infusorian in the same systematic manner that has been adopted 

 in treating of previous genera, because I do not know much about its internal organization ; 

 but in order that the direct alliance of the Flagellata with the Ciliata may be illustrated in 

 this memoir in its strongest light, and inasmuch as Heteromastix is by far the best example 

 of such a transition between the two above-mentioned orders, I shall take the liberty of 

 quoting what I have already published in regard to it in another place. 2 



"Here is an infusorian (figs. 70-74), from fresh water, which, although it has a pretty 

 strong resemblance to Euglena, heightened by the presence of a red eye-spot (s), will be 

 found, upon investigation, to possess some additional and decidedly different characters. In 

 the first place, it has two vibrating lashes (flfl 2 ), which differ remarkably among themselves 

 both in position and character. One of them is always carried in front like a sort of pro- 

 boscis (/), and in fact, it seems to have the office of such an organ, like that of an elephant, 

 to feel and to take hold of objects. I must confess that I was struck with astonishment at 

 the apparent intelligence with which the infusorian extended and twisted and turned and 

 felt about with this extraordinary organ. Never did an elephant seem to use his trunk with 

 more thoughtfulness. With like control did the animal also use the other lash (fl 2 ), always 

 keeping it turned back along the body ; so that it formed a kind of movable keel, when the 

 little creature glided along in its watery element, or was used to sway it from side to 

 side, or oftentimes to raise it up on its tail by forming a prop, as we see it in this other 

 figure (fig. 73.) 



" The motory or propelling power, on the other hand, is restricted, at least in the greatest 

 measure, to another kind of vibratile cilia. These are very short, and are crowded together 

 in great numbers (cl) in a broad furrow or depression (/), which extends over half the length 

 of the body, along its inferior, middle line. When the body is turned over, and the anterior 

 end retracted and swelled out sideways, the furrow (fig. 73,/) becomes quite conspicuous, 

 and the extent of the group of minor cilia (cl) is easily ascertained. They are very minute 

 and in constant motion, propelling the body backward and forward, up and down, to the 

 right or left, according as it is steered by the trailing lash (ft 2 ) which extends along its 

 length. Thus it is, that, although similar in form, a diversity of functions is laid upon these 

 three kinds of cilia that amounts to the most marked specialization, through the simplest 

 means ; in fact, so simple that the eye cannot detect them in any form beside that of pro- 



1 frepos, dissimilar, pann!-, a lash. This genus was originally described in my published volume of Lowell Lectures. Mind 

 in Nature, p. 146, fig. 88. a See note 1. 



