102 PHYSIOLOGICAL SERIES. 



important of which form sphincters. By the contraction of 

 the trunk muscles the water in the pharynx and atrial 

 chamber is forcibly expelled from the atrial aperture, and 

 the animal is in consequence propelled in an opposite 

 dii'ection. The muscle-fibres show a distinct transverse 

 striation. 



Knoll, Deukschr. d. k. Akad. Wiss. Wien, Bd. Iviii. 1891, 

 p. 671. 



C. 53. A preparation of the trunk muscles of Amplrioxus lanceolatus. 

 They consist of a series of open chevron-like muscle-plates 

 (myotomes) arranged parallel to one another along the 

 lateral parts o the body, with their apices directed forward 

 and slightly above the mid-lateral line, those of opposite 

 sides alternating. They are formed of longitudinal fibres, 

 and are separated from one another and from those of 

 the opposite side by a layer of connective tissue. They 

 entirely surround the body with the exception of the 

 ventral area of the atrial chamber, where a layer of 

 transverse muscle is interposed between their ventral ends. 

 The fibres of which these muscles are composed are trans- 

 versely striated and have a highly characteristic plate-like 

 form. The nucleus imbedded in a small quantity of un- 

 differentiated protoplasm lies peripherally. There is no 

 sarcolemma. The middle specimen shows the muscles in 

 position after removal of the integument. .On either side 

 are several isolated myotomes showing their outer (on the 

 right) and inner (left) surfaces. 0. C. 63 A. 



Langerhans, Arch. . Mikr. Anat,, Bd. xii. 1876, p. 291. 



VERTEBRATA. 



FORM AND TEXTURE. 



Texture of Muscle. 



0,54. Portions of muscle from a Cod-fish (Gadus morrhua), 

 which have been steeped in an acid, and reflect iridescent 

 colour in some lights, due to striation producing inter- 

 ference. 0. C. 36. Hunterian. 



