8 THE ROTIFERA. 



studded with what appear to be bright yellow oil-globules. It is divided by an in- 

 itiation at its lower third into an upper portion, the true stomach, and a lower 

 which may be considered to be a short intestine (fig. 1, i). This lower portion frequently 

 lies transversely to the longer axis of the stomach. Both are thickly ciliated on the 

 inner surface, but the cilia of the intestine are larger, and more readily seen. 



When a portion of digested food has been transferred from the stomach to the in- 

 testine, it is kept slowly revolvingby the cilia, till it is suddenly expelled through the cloaca 

 (fig. 1, cl). The intestine is connected with the cloaca by a short and very dilatable tube 

 or rectum (fig. 1, r), and ends (as has been already said) on the dorsal surface, in the 

 median line, just at the commencement of the foot. The rectum also is ciliated, so 

 that the whole of the alimentary tract from the top of the buccal funnel down to the 

 cloaca, with the exception perhaps of the passage through the mastax, is lined with 

 cilia. 



The Vascular System. 



At the right of the intestine (viewed dorsally), and just under the line of the lorica's 

 greatest width, lies the contractile vesicle (fig. 1, cv). This is a delicate bladder which 

 alternately dilates and contracts, and with some regularity. 



The contraction is produced by fine muscular threads, which ramify in its walls, 

 and cause it to empty its contents through a duct into the cloaca. Its distension is 

 most probably due to the fluid poured into it by two looped and twisted tubes (fig. 1, Ic), 

 which may be seen passing to it, one on each side of the body down from the head. 



This is, however, a much disputed question, which will be discussed fully in another 

 place, along with the probable function of the whole apparatus. 



The tubes appear to be surrounded with a granular floccose material, which here and 

 there dilates into irregular masses. Attached to the tubes on each side, at tolerably 

 regular intervals, are five little tag-like bodies (fig. 1, vt), in which a flickering motion 

 may be constantly seen, sometimes presenting the appearance of a waving cilium. 

 There is much difference of opinion about the true structure of these tags — the 

 vibratile tags, as they are termed — but it is probable that their office is to direct the 

 perivisceral fluid into the tubes, and along them into the contractile vesicle, whence 

 it is driven at intervals through the cloaca. 



The Muscles. 



The dorsal muscles are shown in fig. 3, and the ventral in fig. 1. From the posterior 

 dorsal surface of the head, on each side of the cephalic ganglion, and close to it, a stout 

 muscle (fig. 3, l, l) slopes backward towards the dorsal surface, and is attached by a 

 broad base to the lining membrane of the lorica. Outside this pair is a second (fig. 3, 

 2, 2), similarly attached, and running rather obliquely underneath the first pair, but not 

 quite so stout. A similar pair (fig. 4, 4, 4) is attached to the posterior ventral surface 

 of the head, and to the lining of the ventral surface of the lorica. The united action of 

 these three pairs of muscles withdraws the head into the lorica. 



When it is so withdrawn, a pair of diverging muscular threads (not given in the 

 figure) can be seen fixed to the lorica, just below its central notch, with their other 

 ends fastened to the head. These evidently oppose the action of the three other pairs 

 (figs. 3, 1,1, 2, 2 ; 4, 4, 4) and help to draw out the head again. They are assisted in 

 this by a further pair of muscles (also omitted from figs. 3 and 4), each of which 

 is fastened at one end to the base of one of the outermost anterior spines, and 

 at the other to a side lobe of the head. 



But the principal part in driving out both the head and the foot is borne by transverse 

 muscles, which are attached to the lorica at the side, and are closely applied through- 

 out their length to the soft organs of the body. Their sudden contraction compresses 

 the perivisceral fluid, and so forces out the retracted head or foot. Nothing could be 



