424 MR. P. H, GOSSE ON THE STRUCTURE, FUNCTIONS, AND HOMOLOGIES 
bodies causes them to present almost invariably the same aspect to the observer, viz. 
that in which the greatest width is at right angles to the line of vision ; so that we 
may examine specimen after specimen, till patience is exhausted, and acquire no new 
information, because we look each time at the same aspect. 
17 . In the course of experiments with various chemical reagents on these animals, 
I found that a solution of potash had the effect of instantly dissolving the flesh, and 
most of the viscera ; leaving the general integument, the walls of the pharyngeal 
bulb, and ail the solid parts of the manducatory apparatus uninjured*. In most 
cases, also, the last-named organs are expelled from the visceral cavity by the 
contraction of the integuments ; so that they float at large, in brilliant clearness, 
undimmed by intervening tissues, and as patent to observation as when crushed 
between plates of glass ; with the advantage of all the parts being unbroken, and 
retaining their relative positions. Now, by turning the screw of the compressorium, 
flattening or deepening the drop of water, waves were communicated to it, by means 
of which the floating bulb, being nearly globular, was made to revolve irregularly, 
and thus to present, in succession, various aspects to the eye. 
18. The observations which I am about to record were made with one of Powell 
and Lealand’s microscopes, with a power of 560 diameters; except those on Stepha- 
noceros and Diglena, on which the powers employed were 220 and 300 diameters. 
19. For the sake of precision in description, it may be well here to mention a few 
terms that I shall employ, and to define the sense in which they will be used. The 
symmetry of the Rotifera is truly bilateral, the genera Sfephanoceros and Flos- 
culm'ia alone retaining a lingering remnant of radiism, in the arrangetnent of the 
frontal lobes ; even in these, however, the whole of the anatomy besides, both external 
and internal, is bilateral. In most cases this arrangement is obvious ; the motions 
of the animal, like those of the footed larvae of insects, being performed on the belly, 
with the head foremost. Where this is not the case, as with those genera which, 
either with or without an enveloping tube, adhere to foreign substances by the tip of 
the foot, and elevate the body in an erect position, the dorsal aspect is always deter- 
minable by the eye or eyes being towards that surface, by the stomach and intestine 
passing down it, and by the cloaca being on that side of the foot. The ventral aspect 
has the manducatory apparatus, and the ovary. The anterior extremity carries the 
vibratile cilia ; the posterior \'Si terminated by the foot. In such species as are clothed 
with a lorica, I shall call the anterior termination of the dorsum, the occipital edge; 
and the anterior termination of the venter, the mental edge. Other terms will be 
defined in the process of description. 
20. As the manducatory bulb, with its complex contents, is the principal subject 
of these observations, I shall commence with it ; treating the other parts as accessory 
to it. In most Rotifera this organ forms a prominent object, conspicuous from its 
* Dr. Leydig, I find, has used the same agent in examining the teeth in Lacinularia ; but he does not ap- 
pear to have employed it in the investigation of other Rotifera (Siebold and Koll. Zeitschr. 1852). 
