174 



COMPARATIVE PHYSIOLOGY. 



seems to point to ciliary action as falling under the laws gov- 

 erning the movements of protoplasm in general. It is impor- 

 tant to bear in mind that ciliary action may go on in the cells 

 of a tissue completely isolated from the animal to which it be- 

 longs, and though iafluenced, as just explained, by the sur- 

 roundings, that the movement is essentially automatic, that is, 

 independent of any special stimulus, in which respect it differs 

 a good deal from voluntary muscle, which usually, if not al- 

 ways, contracts only when stimulated. 



The lines along which the evolution of the contractile tissues 

 has proceeded from the indefinite outflowings and withdrawals 



of the substance of 

 Amoeba up to the 

 highly specialized 

 movements of a 

 striped muscle-cell 

 are not all clearly 

 marked out ; but 

 even the few facts 

 mentioned above 

 suffice to show gra- 

 dation, intermedi- 

 ate forms. A sim- 

 ilar law is involved 



Pig. 158.— Mode of termination ot tlie motor-nerves (Flint, in the muscular 

 after Rouget). A. Primitive fasciculus of the thyro- j.-Ti 



hyoid muBcle of the human subject, and its nerve- contractility mani- 



tube : 1, 1, primitive muscular fasciculus : 2, nerve- j? j. i u n *j.i- 



tubc ; 3, medullary substance of the tube, Vfhich is lestea by cells Wltn 



seen extending to the teiTninal plate, where it disap- r.+l-ior» -fTTno+irinc 



pears ; 4, termmal plate situated beneath the sarco- "''"'^'^ lUUCWODh. 



lemma— that is to say, between it and the elementary The automatic (self - 

 flbrillte; 5, 5, sarcolemma. B. Primitive fasciculus of • • . j -^ j 



the intercostal muscle of the lizard, in which a nerve- originated, inde- 

 tube terminates: 1,1, sheath of the nerve-tube: 2, -i . ^, .. n 



nucleus of the sheath ; 3, 3, sarcolemma becoming penaent largely 01 



continuous with the sheath ; 4, medullary substance „ o<■^rmllIlc^ vTriT+TiTn 



of the nerve-tube, ceasing abruptly at the site of the ^ hiimuius; rnytnm 



terminal plate; 5, 5, termmal plate; 6, 6, nuclei of the suffffestive of cilia- 

 plate; 7, 7, granular substance which forms the princi- °° 



pal element of the terminal plate and which is con- ry movement, more 

 tinuous with the axis cylinder ; 8, 8, uudnlations ot -j. .. • at,- 



the sarcolemma reproducing those of the fibrilhe; maniiesl; in ine 



9, 9, nuclei of the sarcolemma. earlier developed 



smooth muscle than in the voluntary striped muscle of higher 

 vertebrates, indicating further by the regularity with which 

 certain organs act in which this smooth muscular tissue is pre- 

 dominant, a relationship to ciliary movement something in 

 common as to origin — in a word, an evolution. And if this be 

 borne in mind, we believe many facts will appear in a new 



