236 ZOOLOGY, 



Indeed most mollnsks spawn in the snnuner. Species of 

 Kellia, Galeomma, and Jfonf acuta are viTiparons. 



Some biralTes get their growth in a single year. The fresh- 

 water muscles Hve from ten to twelve years and perhaps 

 longer ; while Trid<u;tui gigantea probably lives from sixty 

 years to a century. Of about 14,000 known species of 

 LameUibrancLs, from SOOO to 9000 are fossil 



Class L— LAMELLIBRAXCHIATA. 



BUati raUjj gffmmetriral moUusks, with two i:alr:esUned hy the mantle, c-jn~ 

 ne(t(d by a dorsal Mnge and ligament; noliead; mouth unarmed., irith 

 tiro pain of labial palpi; inttstint coiled in the ri^.eral mass, uguaUy 

 passing through the rentriele, and alicays ending at the posterior, iiguaHy 

 sipJien-bearing, end of thf body. Foot small, sometimes nearly itariting, 

 never vsed as a creeping disk. V^uaUytwo pairs 'f large Ifof-like giUs on. 

 each side of the tisceral m/iss. Sti-i ■usually in separate indiciduaU. 

 Embryo passing through a so-called morula, gaslrula, and free-rwim ming- 

 nfliger condition. 



Order 1. Asiphonia. — Body-wall or mantle without siphons. Shell 

 sometimes ineqaivalre. (Ostrea, Anomia. Pecten, Melea- 

 grina, Mrtilus, Area, Trigonia, Unio, and Anodonta^'i 



Order 2. ■Siphoniata. — Sipl.ons present. Shell equivalve. (Chama 

 Tridacna, Cardium, Tenus, Mactra, Tellina, S<:ilen, Clava- 

 gelli, Aspergillum.) 



Laboratory Work. — In diss ctinjj the clam, etc., the wort should be 

 performed under water, iu a dissecting trough. One shell should be 

 removed by cutting the adductor by a pointed scaljiel, the mantle dis- 

 sected off and thrown aside, so as to expose the gills, heart, and kid- 

 neys. In dis-^-ectinar the nervous system it is well to introduce a probe 

 into the mouth, and then cut down towards it from above, when the 

 white supraoesophageal ganglia or "brain" will be found, and tli^^ 

 other gfanglia can theuce be traced by the commissures leadinjr from tin' 

 " brain." To find the pedal jranglia and otocyst, cut the foot vertically 

 in two. The heart can be readily found, and the large vein at the base 

 of the gills, but the arterial and venous systems can only well W' 

 studied after making careful injections. For ordinary or even quiti- 

 fine injections, Sabatier used a mixture of lard and turpentine, some- 

 times adding a little suet or wax to thicken the paste, which was 

 colored chrome yellow, vermilion, or blue. For histological exami- 

 nation he used essence of turpentine, colored as befre, or gelatine 



