34 



JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



KEY TO LETTERS. 



aa. Anterior adductor muscle. mp. 



ac. Apical cilia. oc. 



ae. Anterior projection of the mar- oe. 



gin of the mantle. on. 



afm. Anterior foot-muscle. ot. 



ap. Apical plate. pa. 



bg. Byssal gland. pap. 



bl. Blastopore. pc. 



bs. Blood-space. pe. 



eg. Cerebral ganglia. 



cr. Chitinous rods. pfm. 



ec. Ectoderm. pg. 



ep. Epithelium. pn. 



es. Exhalent siphon. r. 



f. Foot. 



g. Gill. rl. 

 gd. Genital duct. s. 

 gs. Gill suspensory membrane. sg. 



h. Heart. st. 

 ie. Inner end of excretory organ. std. 

 int. Intestine. sto. 

 is. Inhalent siphon. t. 

 Ibs. Lower blood-space. ti- 

 ll. Left lobe of liver. ulm. 

 Una. Lower longitudinal muscle. v g- 

 1m. Longitudinal muscle. x - 

 Ip. Labial palp. 



m. Mantle. J- 



mco. Common opening of the excre- z - 

 tory organ and genital duct 

 into the mantel chamber, 



mg. Mid-gut. 



Muscles of the gill plates. 



Otocystic canal. 



Outer end of the excretory organ. 



Otocystic nerve. 



Otocyst. 



Posterior adductor muscle. 



Palp-appendage. 



Pericardial wall. 



Posterior expansion of the mar- 

 gin of the mantle. 



Posterior foot-muscle. 



Pedal ganglia. 



Palp nerve. 



Pouch leading to the cerebral 

 ganglia. 



Right lobe of liver. 



Shell. 



Shell-gland. 



Siphonal tentacle. 



Stomodseum. 



Stomach. 



Test. 



Tentacle nerve. 



Upper longitudinal muscle. , 



Visceral ganglia. 



Depression at the point where 

 the cerebral ganglia are formed. 



Cut wall of gill plate. 



Large cells that appear when the 

 liver is forced into the space 

 dorsal to the intestine. 



