APPENDIX. 139 



less obvious connection with the expansions of tlie lateral canals. But, in one example, 

 which I cannot distinguish from urccularis, the sac is, at its outer extremity, indelinitely 

 expanded, fora and aft, and seems to iBergo into the length of the canal itself, \vliich 

 yet begins clearly in the wall of the head-funnel, and terminates normally in a con- 

 tractile vesicle. 



On the other hand, in Asplanclina, the glands, which arc small oval organs, are 

 connate, on each side of the very long asophagus, remote from, and apparently quite 

 uncomiected with, the canals. 



3. Of the " vibratile tags " I have little to say of direct observation. In rterodina 

 they seem to me wholly wanting. I judge it nearly certain that they are tubular, and that 

 sometlnng is driven through them, whose course is from the lateral canal to the body- 

 cavity.' 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 fuliil some office still, mechanical or vital '? 



4. Of the contractile vesicle, the normal position, form, structure, and function are 

 well known.2 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 Asplanchnce, the organ, though manifest enough, is very small ; in 

 Ifctopidia, as already mentioned, it is only now and then present ; while in Ptcrodina, 

 it is (according to my experience) invariably wanting. 



On the whole, then, I judge that Rotifera possess a well-marked branchial system, 

 which has several striking parallels with that of the Annellida— the Luiubricldca in 

 particular. — P.H.G.] 



THE SETIGEEOUS 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 

 antcnnm 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 

 seta; at their outer extremity. Sometimes they are enclosed in tubular sheaths rising 

 fi-om the surface of the body ; and at others their extremities lie close to apertures in 

 that surface, through which the sets may be seen to protrude. The antennas 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 antennfe ; 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 Philodinada : but in some of 

 these cases their absence may be only apparent ; as the antennre are often reduced to 

 minute setigerous pimples, and so can be easily missed. 



' The perivisceral fluid, or blood, is surely neither effused from the body, nor augmented in quai.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 AsplancUna priodonta, PI. xii. tig. '2c : Cojteus sjncatus, PI. xxx. fig. 7 : and Drachiunus 

 plicatilis (117). 



^ As in Synclicvta pectinaia ; PI. xiii. fig. 3c. " The common case. 



' As in Nolops Brachionus ; PI. xv. fig. 1. ' As in Melicerta ringcns \ PI. v. fig. 4. 



' As in Stephanoccros Eichhornii ; PI. iv. tig. 2. '" As in Ccpeus caudatus ; PI. xvi. tig. 5a. 



