RESEARCH SEMINAR. 233 



the lamellibranchs and the gasteropods ; in the cephalopods it 

 does not exceed 0.02" ; in the crustaceans it does not exceed 

 o.oi". The latent period of the heart-muscle is not greater than 

 that of the body-muscle of the same animal. 



4. The rate of propagation of the contraction in the tunicate 

 heart (Ciona) varies from 200 to 350 mm. per sec. 



5. The molluscan, the arthropod, and the tunicate heart ex- 

 hibits a condition of reduced excitability at the beginning of 

 systole, but no refractory period in the sense of inexcitability. 



6. The molluscan, the arthropod, and the tunicate heart, that 

 is greatly fatigued or injured, and in poor condition so that it does 

 not beat spontaneously, responds to stimuli of increasing in- 

 tensity with contractions of increasing amplitude ; but the pul- 

 sating heart or the quiescent heart whose excitability is not greatly 

 reduced tends to respond with contractions of uniform amplitude 

 to stimuli of increasing intensity within a wide range, but in- 

 creasing the strength of the stimulus above this range is followed 

 by supermaximal contractions. The " all-or-nonc ' law does 

 not apply. 



/. In the molluscan and the crustacean heart a strong induced 

 shock sent through the heart at the beginning of systole dimin- 

 ishes the strength of that beat. 



8. The molluscan, the arthropod, and the tunicate heart is 

 inhibited in diastole by the interrupted current of a certain inten- 

 sity applied directly to the heart. This inhibition is obtained in 

 hearts apparently not provided with inhibitory nerves, and in 

 hearts provided with inhibitory nerves after these have been para- 

 lyzed by the action of drugs. It is therefore an action of the 

 induced current directly on the rhythmical tissue. 



9. The molluscan, the arthropod, and the tunicate heart can 

 be tetanized. 



July 15. Feeding Experiments for Determining the Life His- 

 tory of an Oyster Parasite. By D. H. TENNENT. 

 The experiments described were conducted for the purpose 

 of determining the adult form and the life history of the trema- 

 tode, of which BucepJialus haimeanns Lacaze Duthiers {Buceph- 

 alus cucullus McCrady), abundant in oysters of various regions, is 

 the cercaria. 



