40 WILLIAMS : PHENOMENA OF MUSCLE-CONTRACTION. 



cilia, such as that produced by an impulse of a fluid current, 

 aids in a marked degree the activity of the cilia. The first 

 observer of ciliary movement was A. de Heyde, in 1683. Since 

 then many observers have worked well in this direction, such as 

 Sharpey, Valentin, Purkinje, Virchow, Kistiakowsky, Roth, 

 Engelmann, Stuart, Neumann, Huzinga, Kiihne, Bowditch, and 

 Calliburces. 



Secondly, with regard to the second group — muscular 

 CONTRACTION PROPER. In mammalian muscle the fibres are 

 of two kinds, striated and unstriated. The striated muscle- 

 fibres are elongated, about one-and-a-half inches in length, and 

 more differentiated in character than the unstriated which are 

 fusiform in shape and about g-^y inch in length. The former 

 kind are found in those portions of the body where active and 

 rapid movements are effected, the latter where much slower 

 movements are needed. The fibres of the molluscan muscle 

 are unicellular and unstriated, and consequently not so differen- 

 tiated from protoplasm as the striated and unstriped vertebrate 

 muscle-fibres. And since it is a physiological law that the more 

 rapid the contraction the muscle performs the more differen- 

 tiated in character are its fibres from the ordinary type of 

 protoplasm, the features of muscle-contraction in the moUusca, 

 we should naturally expect, would not be so well pronounced as 

 those attending the contraction of the two kinds of muscle-fibres 

 in the mammalia. This, however, is evident on seeing a snail 

 crawl, the slow locomotory movements of which have earned for 

 it the sobriqtiet of "tardy-gaited." The latent period, i.e. the 

 time which elapses during the passage of the wave of change 

 along the nerve to the muscle and the chemical changes going 

 on in the muscle previous to contraction — we also should expect 

 to be longer, and we are not deceived, for in the vertebrates this 

 is about Y^o sec. in striated and -^-^ sec. in unstriated muscle, 

 and H. Varigny ^ has shown that in the mollusca it varies from 



^ " Sur la periode d'excitation latente de quelques muscles lisses de la 

 vie de relation chez les invertebres." Compt Fend, ci, pp. 570—572. 



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



