ANIMAL KINGDOM. 233 



tricle. The cerebral ganglion is still placed on the oeso- 

 phagus; but the nervous system becomes more compli- 

 cated, always indeed consisting, it is said, of at least two 

 ganglions, to wit, the cerebral and visceral. The liver is 

 more voluminous, but otherwise is but little different from 

 that of the Ascidia. The Acephala are perfect herma- 

 phrodites, that is, sufficient of themselves for all the pur- 

 poses of generation, and their young pass some time in the 

 substance of the branchiae before they are sent into the 

 world. 



Such is a very rude sketch of the characteristic proper- 

 ties of beings which will always attract some portion of 

 interest, whether we consider their beauty or utility. 

 The Acephala indeed may be said to comprise all the 

 animals of the great division MoUusca that are particu- 

 larly useful to mankind. The Oyster is a good exam- 

 ple of the group. But there are some, as has already 

 been stated, whose mantle having its lobes united in front 

 possess shells open at the lateral extremities, so that the 

 whole body becomes as it were tubular. Such is the 

 family of Solenacece Lam. They are in fact animals, as 

 Lamarck says, whose width has become excessive, while 

 what, properly speaking, is their length has been pro- 

 portionably reduced. We are led thence to the genus 

 Pholas, extraordinary on account of the accessory pieces 

 of shell which cover its hinge. These accessory pieces 

 have however nothing to do with the ligament of the bi- 

 valve, as M. Lamarck has shown. Among the Acephala 

 are also the well known ship worms {Teredo navalis Linn.) 

 which, notwithstanding their vermiform appearance, are 

 true bivalve MoUusca, whose shells are become too small 

 for their body, while the exterior accessory pieces which 



