VIII 



PHYLUM MOLLUSCOIDA 



335 



mth- 



passing upwards from the mouth, an expanded stomach, (sf) and ;i 



straight intestine (int.} which extends from the stomach downwards 



and backwards towards the ventral surface and ends blindly, 



there being no anus. On 



each side of the stomach 



and opening into it by a 



duct, is a large, branched 



digestive gland (d. <?/). The 



whole canal is lined with 



ciliated epithelium. 



The body-wall consists 

 externally of an epidermis 

 formed of a single layer of 

 cells, then of a layer of 

 connective tissue, of a car- 

 tilaginous consistency in 

 many parts, and finally of a 

 ciliated ccelomic epithelium 

 lining the body-cavity. On 

 the outer surfaces of the 

 mantle-lobes,where they are 

 in contact with the shell, the 

 epidermis is replaced by a thin membrane showing no cell structure. 



The muscular system (Fig. 268) is well developed. Two large 

 adductor muscles (ad. in) arise on each side from the dorsal valve 



Fin. -2(\~. Magellania flayescens, the ventra 



valve removed ; /. p. cardinal process ; IpJi. arm 

 of lophophore ; I ph.' 1 its coiled process having 

 the tentacles removed on the right side ; mth. 

 mouth. (After Davidson.) 



d.v 



ad.m, 



nth 



d.m. 



FIG. 26S. Muscular system of Magellania. <'. /. adductors ; d. beak ; <l. j. in. dorss 

 adjusters; d. m, d. m' divaricators ; d. r. dorsal valve; int. intestine ; mth. mouth; /'. 

 peduncle ; pd. sti. sheath of peduncle ; p. m. protractor; at. shelly loop ; r. . j. m. ventral 

 adjusters ; ;. v. ventral valve. (After Hancock.) 



and, passing downwards, unite with one another so as to have a 

 single insertion on the ventral valve : their action is to approxi- 

 mate the valves and so to close the shell. A large and a small 



