434 GEIS^ERAL HISTORY OF THE INFUSORIA. 



ramified vessels ceases to be easy of demonstration. They still form one 

 system ; but the ciha are no longer to be fonnd in the smaller ramified vessels. 

 In certain Nematoidea the vascular system is reduced to a couple of lateral 

 contractile vessels altogether devoid of cilia, but communicating with the 

 exterior by a small apertm-e. Now in all these cases there is no doubt the 

 vascular system is, physiologically, a respiratory and j^erhaps a urinary system, 

 while the common cavity of the body represents the blood-vascular system of 

 the Mollusca and Articulata. If this system, then, be not at all homologoiLs 

 with the blood-vascular system of the higher Annulosa, it is so with the 

 tracheae of Insecta." 



We may repeat here that the delicate and ciliated rotary organ must in 

 some measiu-e subserve the purpose of respiration, after the manner of the 

 gills of a reptile or of a fish, by providing for the aeration of the hquids 

 contained within it through the agency of the constantly renewed contact of 

 fresh water flowing over its actively- vibratile surface. 



OF THE NEEVOUS SYSTEM AND THE ORGANS OF SENSE ; PSYCHICAL 

 ENDOWMENTS. 



a. Of the Nervous System. — The existence of a rudimentary nervous 

 system is now universally admitted ; but at the period when Dujardin wrote, 

 that talented observer felt that the state of knowledge respecting the Rota- 

 toria was not sufficiently precise to estabhsh the existence of nerves and of 

 nervous ganghons. His scepticism was, no doubt, increased by observing the 

 imphilosophical facility with which Ehrenberg described and represented 

 nerve-cords and ganglions according to preconceived notions and loose ana- 

 logies. Illustrations of Elu^enberg's supposed nervous apparatus, and of its 

 modifications of form in different animals, are to be found in his descriptions 

 of every family and genus. Thus in giving the characters of Lacinidaria, he 

 says that '' near the oesophagus is situated a nervous mass, the analogue of 

 a brain chvided into four or six lobes ; also, as in Megahtroclia (XXXII. 374), 

 two ring-like and radiating masses with a row of ganglions Ijing beneath the 

 muscles of the cihary wreath." In Mellcerta, he speaks of a ciu'ved gland- 

 like band of nerve-matter ; in Etiterojplea, which has no eyes, of a brain-like 

 knot, sending off a thick tortuous nerve-cord along the dorsal siu-face to the 

 second transverse vessel, where the rcspii'atory opening probably exists ; of a 

 ganglion placed beneath the e3^e in twenty-six species of Notommata, which 

 in N. Copeus and N. centnira is three-lobed and seated above the maxillary 

 bulb, whilst in the remainder it consists of one or more nervous gangha 

 seated amidst the muscles of the cihary apparatus ; and in Otoglena, of an 

 oval cerebral ganglion with two dark appendages, a red eye, a long neiTC- 

 loop in the neck, with a prolongation backward, a forked ventral nerve, and 

 two ear-shaped frontal protuberances bearing two visual points. 



It would be useless to multiply these references ; the general deduction 

 from the many descriptions of Ehrenberg is, that there exists a cerebral or 

 brain ganghon, which supports the eyes, and by its extension enciiTles the 

 CBSophagus like a loop, sending off nerve-cords in every dii'ection, and often 

 complicated by the presence of other nerve -ganglions about the head, neck, 

 and body. Moreover, the apparent reticulations frequently visible below the 

 ciliary wreath, which he sometimes viewed as a vascular network, he at 

 others spoke of as a nervous plexus. 



The present prevaiHng opinion is similar to the above, viz. that there exists 

 a brain or central nerve-ganglion above the oesophagus, with outgoing nerve- 

 fibres, and sometimes accompanied by supplementary ganglia in other regions. 

 Xevertheless the special descriptions of Ehrenberg arc not accepted ; the 



