2;u 



VEi;TEIil!ATI>: ANIMALS. 



ijii euoli siile. The water is taken in at the mouth b}' a process 

 aualoyonw t<i swallowing, ami it gains admission to tlie branchial 

 cliambers by me:ins of a scries of elefts or slits which jierforate the 



sides of the |)haiTnx. Having 

 li.'isseil over tlie gills and lost 

 its oxygen, tlie etf'ete water 

 makes its est;a|i(_' behind ])V 

 an aijerture called the "gill- 

 slit," whii/li is jilaced on the 

 side of the neck. The ojien- 

 ing of the gilbslit is closed in 

 front Ijy a ehain <ii Ihit bones 

 whidi Constitute the "gill- 

 cover," and by a memljrane 

 whicli is .snpiiorted upon a 

 varialile nundier of .slender 

 bony spines. This is the gen- 

 eral mechanism of respiration 

 in one of the Bony Fishes, 1 >ut 

 difi'erent arrangements are 

 found in other case.s, which 

 will be sidjseipientl}' noticed. 

 The Ai'art in fi,shes may 

 be regarded as essentially a 

 liranchial or respiratory heart, 

 being concerned chiefly witii 

 driving the venous and im- 

 ])ure blood to tlie gills. It 

 consists in almost all cases of 

 two c.-ivities, an auiicle and 

 a ventricle (hg. l(i!)). The 

 auricle {<iii) receives the ven- 

 ous blood which has pa.ssed 

 tlii'ongh all the v.arious parts 

 of the body, and propels it 

 into the ventricle (r). From 

 the \entricle proceeds a single 

 great vessel (the " br;inchi,-d 

 artery"), the base of whicli is 

 usuidly dcvelopeil into ;i mn.s- 

 ((('/), wliirh arts ,-is a. kind of 

 ■I.' anil I, nil,, IX iirlrridxiis the 

 where it is subjected to the 

 1 blooil is not returned to the 



