716 CLASS XII. 



nerve-mass, the par pedale. t also connected with the first ganglia by 

 two shorter strings, is, in those genera that have no foot, feebly 

 developed, or according to GARNER, even absent. The nerve- 

 ganglia are usually distinguished by a red or orange colour 1 . The 

 nervous system of the Brachiopoda is not yet perfectly known, but 

 seems to be formed after a different typus 2 . 



Amongst the parts which may be regarded as the seats of senses, 

 the conical cirri are first to be noticed, which are present sometimes 

 along the entire margin of the mantle of the Lamellibranchiata, or on 

 some parts of the mantle, at the opening of the siphon for example, 

 and which in the Brachiopoda are changed for long, stiff, glistering 

 hairs. The mouth, moreover, in the Lamellibranchiata is surrounded 

 by two pairs of transversely striped organs of touch of considerable 

 size, triangular, elongated or oval laminas, which some consider to 

 be accessory gills, from their external resemblance to these organs. 

 In the Brachiopoda there are two long arms, beset pectinately with 

 filaments like a fringe, situated at the side of the mouth, where 

 they are rolled up in a spiral form, and concealed within the shell. 

 Organs of vision have, of late years, been shewn by microscopic 

 investigation to be present in Pecten, Spondylus, and many other 

 genera amongst the Lamellibranchiata, as green, red-yellow, or 

 brown tubers, shining brightly, and often set upon a small pedicle 

 at the margin of the mantle. In different species more than a hun- 

 dred such eyes have been counted 3 . 



1 Compare K. GARNER On the nervous system of Molluscous Animals, Trans, of Linn. 

 Soc. xvn. 1835, PP- 485 488, PI. 24; BLANCHARD Observations surle Systeme nerveux 

 des Mollusques lamellibranches, Ann. des Sc. not., 3ieme SeVie, in. 1845, pp. 321 340, 

 PI. 12. Here may be found a copious historical review of this subject. The two small 

 nerve-ganglia that lie near the oval ganglia in Ostrea (BRANDT and RATZEBU RG Medizin. 

 Zool. IT. s. 340, 341), BLANCHARD regards as answering to the^ar pedale (here want- 

 ing according to GARNER). Nervous branches that arise from the lateral commissural 

 string of the first and hindmost pair, on which in some species (Solen, Area) even gan- 

 gliform swellings are observed, correspond, so it appears, to the sympathetic nervous 

 system of articulate animals, especially to the lateral portions of it in the crays, which 

 in like manner arise from the collar round the neck (see above, p. 618). Those lamelli- 

 branchiates, which are provided with a tubular prolongation of the mantle, have often 

 between the muscles, that retract the tube, small nerve-ganglia in addition. 



2 CUVIER Mem. sur la Lingule, p. 8, speaks very indecisively on this point ; OWEN 

 describes a nerve-ganglion between the basal pieces of the two arms, and two others at 

 the side of the mouth. Trans, of Zool. Soc. I. p. 156. [On the nervous system of Tcre- 

 bratula see OWEN Introduct. &c. pp. n, 12 (cited above, p. 710).] 



3 POLI spoke of such eyes smaraydino colore coruscantes, which are situated on the 

 larger cirri of the border of the mantle in Spondylus (n. p. 107) and Pecten Jacobceus 



