50 WILLIAMS : PHENOMENA OF MUSCLE-CONTRACTION. 



Pecten have been found by R. Blanchard ^ to be striated (though 

 the strise are not identical with those in the striated vertebrate 

 muscle-fibres, yet this shows a differentiation), and that there is 

 a possibility that the same muscles of the other bivalves men- 

 tioned may be striated also. He did not, however, find this in 

 Mytilus, Unio, or Anodonta. A. Coutance ''' has also found that 

 a weight of 10,000 grammes, is needed to open a contracted 

 Pecten weighing 85 grammes without the shell, and that then 

 the muscles rupture, while an oyster weighing 12 grammes, 

 without the shell needed the traction of 10 kilogrammes to 

 close its valves. Striation in the muscle-cells has also been 

 observed in the odontophore of Haliotis and Patella, in a 

 species of Acmsea by Dall,® and in the heart of Pecten, Ano- 

 donta, Helix, and Aplysia by J. Dogiel.^ And, according to 

 Pawlow, ^° two kinds of nerve-fibres supply the adductor 

 muscles of Anodonta cygnea — one inhibitory, the other motor. 

 The motor nerves spring from the ganglia next to the muscles, 

 and carry contracting impulses ; the inhibitory fibres pass from 

 the two anterior ganglia only, and bear relaxing impulses. Prof. 

 Hartmann ^ ^ also states that he has observed the prunitive 

 fibrillcB of the muscles of Cephalopods to contract. During 

 contraction the muscles become shorter and correspondingly 

 thicker, oxygen is absorbed and carbonic dioxide excreted as 

 a waste tissue product, and the temperature rises. Glycogen 



* "Note sur la presence de muscles stries chez les moUusques acephales 

 monomyaires. " Rev. Int. Sci., 1880 (No 4) ; also Constance, in Bull. Soc, 

 Brest, 1879; abstr. J. R., Micro. Soc, iii, p. 930. 



' " De I'energie et de la structure musculaire chez les moUusques ace- 

 phales." Paris; 1878; 8vo. 



* American Journal of Science, Feb., 1871, p. 123; also Af/ierican 

 Naturalist, iv, p. 691. 



° "Die Muskeln und Nerven des Herzens bei einigen mollusken." 

 Arch. Mikr. Anat., xiv, pp. 59 — 65. 



10 «<wie die Muschel ihre Schale offnet Versuche und Fragen zur 

 Allgemeinen Muskel-und-Nerven-physiologie." Arch. Ges. Phys., xxxvii, 

 pp. 6 — 31 ; abst. Nature, xxxiii, p. 106. 



" S. B., Nat. Fr., 1873, p. 94. 



J.C. vi., Jan., 1889. 



