VIII 



PHYLUM MOLLUSOOIDA 



335 



passing upwards from the mouth, an expanded stomach, (st) and a 



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. gl~). 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 coelomic 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. m} arise on each side from the dorsal valve 



ad.m 



'.sh. 



Fj<;. _',:. Magellania flayescens,the ventral 

 valve removed ; c. p. cardinal process ; Iph. arm 

 of lophophore ; Iph. 1 its coiled process having 

 the tentacles removed on the right side ; mth. 

 mouth. (After Davidson.) 



dim, 



FIG. 268. Muscular system of Magellania. ad. m. adductors; b. beak; d. aj. m. dorsa 

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

 peduncle ; pd. sh. sheath of peduncle ; p. m. protractor ; si. shelly loop ; i: a. j. m. ventral 

 adjusters ; v. 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 



