436 OENEKAL HISTORY OF THE INFUSORIA. 



*' I believe that this is, in fact, the true nervous centre, and that the sac 

 in connexion with it is analogous to the ciliated pits on the sides of the head 

 of Nemertidce, to the ' ciliated sac ' of the Ascidians, which is similarly con- 

 nected with their nervous centre, and to the ciliated sac which forms the 

 olfactory organ of AmpMoxus. 



*' Mr. Gosse has described a similar organ in MeUcerta ring ens ; and I have 

 had an opportunity of verifying his observations, with the exception of one 

 point. According to this observer, the cilia are continuous from the trochal 

 disk into the cup ; so far as I have observed, however — and I paid particular 

 attention to the point, — the cilia of the cup are wholly distinct from those of 

 the disk. The interesting observations of the same careful observer, upon the 

 architectural habits of MeUcerta, would seem to throw a doubt upon the pro- 

 priety of ascribing to the organ in question any sensorial function. But 

 however remarkable it may seem that an animal should build its house with 

 its nose, we must remember that a similar combination of functions is ob- 

 vious enough in the elephant." 



This last analogy is assuredly very far-fetched, and can serve nothing in 

 the argument ; and to us it seems a much more reasonable supposition that 

 the homogeneous bilobed body below the ciliated cup is a gland, than that it 

 is a brain ; were it a brain, surely some nerve-iibres would be traceable from 

 it into the interior of the animal. Of this body Prof. Williamson says — " I 

 see no sufficient reason for assigning to the small organ nervous functions ;" 

 and he further remarks that "the ciliated sac or cup becomes so contracted when 

 the animal is not busy in constructing its case, as to be almost invisible," which 

 is another circumstance discountenancing Prof. Huxley's notion of its pur- 

 pose. Cohn has no doubt of the cerebral nature of the large semiglobular 

 mass, noticed also by Ehi^enberg, in the head of Hydatina senta ; and he 

 records having frequently observed in its interior a large, transparent, circu- 

 lar vesicle or vacuole. A large number of nerves are given off from its an- 

 terior portion ; but from its posterior, two thick fibres proceed backwards and 

 outwards to the apparent ciliated opening on the surface of the back, and 

 constitute a cervical loop. There is, however, no actual opening, but merely 

 a ciliated fossa, which is probably a sentient organ. About the large cerebral 

 ganglion are other lobules, also probably nervous, from which fibres are given 

 off and possibly form a plexus between the alimentary tube and ovary, be- 

 sides supplying the muscles. Above the ciliated fossa named, is another de- 

 pression supplied with nerves ; and, according to Ehrenberg, a similar one 

 is present on the oj^posite side of the bod)*. 



Various accessory ganglions or nerve-centres have been represented by 

 authors at different parts of the body, mostly in relation with some of the 

 principal organs, this arrangement being suggested by the known nervous 

 system of other Invertebrata — for instance, the Mollusca, which have usually 

 a special ganglion for the nervous supply of each principal organ of the body. 

 Such a multiplication and disposition of ganglia, Oscar Schmidt endeavoured 

 to demonstrate in BracMonus urceolaris and in Hydatina senta. His inter- 

 pretation has, however, not been accepted by others, and, generally, the 

 characteristics of ganglions are so ill-defined, that the bodies considered to 

 be such by the obsei^er are pronounced to be no other than vacuolar thick- 

 enings of connective or other dissimilar tissue by others. 



Perty makes the statement that in Rydatina, Synchceta, and Diglena there 

 is a series of ganglions along the anterior surface of the abdomen, with con- 

 necting nerve-fibres between them and the brain. A nervous system of this 

 sort belongs to the higher Crustacea ; but although many have sought it in 

 the Rotatoria, Perty is the only observer who has affirmed its existence in any. 



