INTRODUCTION. 9 



more effective than this hydrostatic pressure ; and under it the retracted foot darts out 

 of the lorica with amazing swiftness. 



When the head is protruded, and the cilia are all in full play, Brachionus may often 

 be seen to move its head, without withdrawing it, first to one side and then to the other, 

 depressing the side lobes alternately. This action is effected by two pairs of short 

 muscles (figs. 3, 4, 3, 3). one on each side, attached to the lorica at about one-third of its 

 length from the front, and at their anterior ends inserted into the side lobes. 



Just as the muscles attached to the dorsal surface control the action of the head, so 

 do the majority of those of the ventral surface give its various motions to the foot. 

 They are six in all. First, two central muscles, closely parallel (fig. 4, 5, 5), and each 

 divided into two branches at its upper end, run from nearly the middle of the lorica 

 down to the bottom of the foot, where they appear to be attached each to one of the 

 toes. Next, two slighter ones (fig. 4, 6, e), which pass up from the base of the toes, 

 one on each side of the foot, and then diverge right and left from the central pair to 

 points on the lorica about half-way between the median line and its edge. Besides 

 these, there is, attached to the upper end of the foot and on each side of it, a muscle 

 (fig. 4, 7, 7) which diverges still farther from the median line, and is fastened not far 

 from the margin. All these six can act together, so as to draw the foot suddenly 

 within the lorica ; while, by contracting some and relaxing others, the animal can 

 whisk the foot about, or, if the toes be adherent to any substance, can shake its whole 

 body vigorously from side to side a favourite action. 



The Nervous System and Organs of Sense. 



The nervous system is represented by a bean-shaped cephalic ganglion (figs. 11, 1, gn) 

 seated within the head on its dorsal side. Its substance is marked with what appear to 

 be the hexagonal boundaries of cells. It is two-lobed posteriorly, and on the niche 

 between the lobes lies the crimson eye (fig. 11, e). 



The pigment is distinctly curved round both sides of the niche so as to lie on each 

 lobe, and to give rise to the notion that the eye may really represent a pair fused into 

 one. I have not detected in this Rotiferoii the clear spherical lens which is so plainly 

 visible in some of the others. 1 Attached to the upper portion of the cephalic ganglion 

 on the dorsal side is a conical and very flexible tube (fig. 1, a), whose broad base rests 

 on the ganglion, and whose free end passes through the sinus in the lorica between the 

 two longest spines. This is the dorsal antenna. A bulb armed with motionless setae 

 completely closes the orifice of the tube ; and is so attached to its rim, that when this 

 bulb is withdrawn by the contraction of a muscular thread fastened to its base, the 

 tube is drawn down also by being infolded like the finger of a glove (fig. 15). 



There are two other setigerous bodies, close to the dorsal surface of the lorica, 

 and with the setae protruding through the surface. They are near the margin on each 

 side, a little above the line of greatest breadth (fig. I, a'}. They are rocket-shaped struc- 

 tures, the cylindrical heads carrying on their blunt, rounded, outer ends, radiating setas ; 

 and giving off, from their inner and pointed ends, cords which can be traced but a little 

 way below the surface. 



But the list of the tactile organs of BracJiionus is not yet exhausted. From the two 

 spaces on the dorsal side of the corona lying between the three large setigerous promi- 

 nences (fig. 1, sp] rise two papillae, each bearing a long and very flexible style (fig. 1, ts). 

 A similar style (fig. 2, t's') is placed on the ventral side, just within the rim of each ciliary 

 circlet ; and another pair on the top of the central prominence. The whole six are 

 very mobile ; and, from the way in which they seem to be used to explore in all direc- 

 tions, there is little doubt that they are organs of touch. 



1 As in Pcdalion, Conochilus, &c. 



