APPENDIX. 139 
less obyious connection with the expansions of the lateral canals. But, in one example, 
which I cannot distinguish from wrceolaris, the sac is, at its outer extremity, indefinitely 
expanded, fore and aft, and seems to merge into the length of the canal itself, which 
yet begins clearly in the wall of the head-funnel, and terminates normally in a con- 
tractile vesicle. 
On the other hand, in Asplanchna, the glands, which are small oval organs, are 
connate, on each side of the very long esophagus, remote from, and apparently quite 
unconnected with, the canals. 
3. Of the “‘ vibratile tags” I have little to say of direct observation. In Pterodina 
they seem to me wholly wanting. I judge it nearly certain that they are tubular, and that 
something is driven through them, whose course is fvom the lateral canal to the body- 
cayity.! Assuming that the function of the system is the separation of oxygen from the 
water, may it not be that the tags are reservoirs in which pure oxygen collects, and 
from which it is pumped into the perivisceral blood, while the hydrogen left pursues its 
course, perhaps to fulfil some oftice still, mechanical or vital ? 
4. Of the contractile vesicle, the normal position, form, structure, and function are 
well known.? But in the two largest species of Salpina, macracantha and eustala, there 
are two of these organs, of ample dimensions, one on each side, into which the com- 
paratively straight and thick lateral canals empty by trumpet-mouths. Strange to say, 
in the former species the “ gastric glands’ seem wholly wanting. 
In the great Asplanchne, the organ, though manifest enough, is very small; in 
Metopidia, as already mentioned, it is only now and then present; while in Pterodina, 
it is (according to my experience) invariably wanting. 
On the whole, then, I judge that Rortrera possess a well-marked branchial system, 
which has several striking parallels with that of the ANNELLIDA—the Lumbricide in 
particular.—P.H.G.] 
THE SETIGEROUS SENSE-ORGANS. 
The nervous system of the Rotifera is simple. It consists of one nervous ganglion 
situated on the dorsal side of the buccal funnel, usually near the mastax ; and sending 
out nervous threads to the eyes,® and to certain organs of sense, which have been termed 
antenn@ or tentacles as they are possibly tactile organs; but whose function is by no 
means certain. They consist of knobs or cylinders, which usually carry a bunch of fine 
sete at their outer extremity. Sometimes they are enclosed in tubular sheaths rising 
from the surface of the body; and at others their extremities le close to apertures in 
that surface, through which the set may be seen to protrude. The antenne are in two 
pairs. Of these the upper pair is invariably dorsal; and its constituents, though some- 
times widely separate,‘ are most frequently pressed close together,’ or fused into one.® 
The lower pair is to be found sometimes on the dorsal surface,’ sometimes on the 
ventral,’ and sometimes on the line between the two.’ In one case this lower pair is 
also fused together,!" and the creature has but two antenne ; both dorsal, and both on 
the median line. It is only necessary to add that, in many species, one or other pair 
appears to be absent ; notably the lower pair in all the Philodinade: but in some of 
these cases their absence may be only apparent; as the antenne are often reduced to 
minute setigerous pimples, and so can be easily missed. 
1 The perivisceral fluid, or blood, is surely neither effused from the body, nor augmented in quat.tity, 
sensibly. 
? Since a special reservoir would seem needless for the mere discharge of the effete water, an urinary 
office may belong to this bladder. 
* When there is only one eye it is generally seated on the nervous ganglion itself. 
* As in Asplanchna priodonta, Pl. xii. fig. 2c: Copeus spicatus, Pl. xxx. fig. 7: and Brachionus 
pricatilis (117). 
5 As in Syncheta pectinata ; Pl. xiii. fig. 3c. 6 The common case. 
7 As in Notops Brachionus; Pl. xv. fig. 1. 5 As in Meliccrta ringens ; PI. v. fig. 4. 
° As in Stephanoceros Eichhornii; Pl. iv. fig. 2. ' As in Copeus caudatus; Pl, xvi. tig. da. 
