April 3, 1903.] 



SCIENCE. 



549 



Loligo pealii attracted my special attention, 

 because its reactions to electrical stimulation 

 did not seem to fall in line with the peculiari- 

 ties of cardiac muscle just referred to. The 

 Loligo ventricle responded to the interrupted 

 current of sufficient intensity with a continu- 

 ous, to all appearance, tetanic contraction, 

 minimal stimuli were by no means ' at the 

 same time maximal; and a refractory period 

 or a state of inexcitability seemed not to be 

 present. 



This led to the examination of the hearts 

 of the following invertebrates on these three 

 points : 



Tunicata : 



Clavelina sp. 

 Mollusca : 



Octopus punctatus. 



Loligo pealii. 



Ariolimax colurnbianus. 



Limax maximus. 



Pleuroiranchcea sp. 



Doris sp. 



Janus sp. 



^olus sp. 



Ualiotis craceropodii. 



Haliotis rufescens. 



Lucapina ci'enulaia. 



Gryptochiton stelleri. 



Mytilus calif ornianus. 



Mya arenaria. 

 Arthropoda : 



Cancer antennarius. 



Brachynotus nudis. 



Pachygrapsus crassipes. 



Epialtus productus. 



Owing to the delicate structure of the ven- 

 tricles of Clavelinq, and the nudibranchs (with 

 the exception of a species of Doris) their con- 

 tractions could not be recorded by the ordi- 

 nary graphic method, but direct observation 

 had to suffice. The ventricles of all the other 

 species worked on were suspended and their 

 reactions recorded by a light lever. But ex- 

 periments were also performed on the ven- 

 tricles in situ, as check on the graphic record. 



1. In all the forms experimented on an 

 intensity of the interrupted current was 

 found to which the ventricles responded with 



a continuous maximal or supermaximal (as 

 compared to the normal) contraction during 

 its application. By varying the intensity 

 and the rapidity of succession of the shocks 

 superposition and partial fusion of the indi- 

 vidual contractions were obtained (except in 

 Crypiochiton and in some of the nudibranchs) 

 similar to those of the skeletal muscle of 

 vertebrates. The continuous contraction ap- 

 peared to be truly ' tetanic ' in character, ex- 

 cept in case of Crypiochiton and some of the 

 gastropods. The intensity of the interrupted 

 current required to call forth the continuous 

 contraction was considerably greater than suf- 

 ficed to tetanize the body muscles in the sam.e 

 animal. 



2. If by the refractory period is meant a 

 state of inexcitability, I have so far been un- 

 able to demonstrate its presence in the ven- 

 tricles of this series, for an intensity of the 

 stimulus can in every case be found sufficient 

 to affect the hearts in any phase of rhythmic 

 contraction; but a period of reduced excita- 

 bility, maximal during the systole, seems to 

 be present in the case of the decapods, the 

 cephalopods and in several of the gastropods. 



3. Nor does the ' all or nothing law ' apply 

 to the hearts of this series of invertebrates. 

 But as regards this relation of the magnitude 

 of contraction to the intensity of the stimulus, 

 there is a great difference between the ven- 

 tricle of Cryptochiton on the one hand and 

 that of Octopus or Cancer on the other. The 

 Octopus ventricles seem to come nearest to 

 the vertebrate heart on this point, while the 

 ventricle of Cryptochiton in no wise appears 

 to partake of this property of vertebrate car- 

 diac muscle. With the exception of Crypto- 

 chiton and Doris the hearts give uniform 

 beats to stimuli of considerable range in in- 

 tensity, but increase in the intensity above 

 this range is followed by increase in the height 

 of contraction. In Octopus increase in the 

 intensity of the stimulus above a certain 

 strength seems to decrease the magnitude of 

 contraction. 



4. If the interrupted current is too weak 

 to produce acceleration of the beats or the 

 continuous contraction, it produces inhihition 

 in diastole during its application to the ven- 



