1873.] 127 [Putnam. 



EXPLANATION OF PLATE II. 



The drawings are all from fibres of the Gyrinus, as seen with objective 10 im- 

 mersion, and No. 3 eyepiece (Hartnack), and are slightly reduced. 



-Fig. 1. Muscular fibre at rest under normal conditions, showing the various 

 appearances of the granular and bright bands. 



Fig. 2. A fibre at rest at A, contracted at B, and stretched at C. 



Fig. 3. A fibre in passive contraction (second state) attached to a tendon. 



Fig. 4. A fibre teased out in glycerine. 



The drawings are more or less diagramatic, owing to the great difficulties which 

 the object presents. This is particularly the case at B, in fig. 2, and can easily be 

 accounted for when it is remembered that the wave of contraction is never sta- 

 tionary for a second. The gray at C, in fig. 2, is too dark. 



Notes on the Genus Myxine. By F. W. Putnam. 



The specimens which I have the pleasure of bringing before the 

 Society to-night belong to a most interesting genus of fishes, and are 

 the second stage in the development of the great branch of the ani- 

 mal kingdom which reaches its culmination in man. The only lower f 

 form of vertebrates known is the single species, which has the 

 characteristics of a vertebrate animal of such an elementary struc- 

 ture, or entirely suppressed, as to induce Professor Haeckel to sepa- 

 rate it from all other vertebrates as a primary division of the branch . 

 under the name of Leptocardia. 



In the animals before us we find a most lowly organization, but 

 still everything in their structure is markedly of the vertebrtite type, 

 and no one can hesitate as to their position in the system being 

 above the lancelet, and below the lampreys. 



As my object to-night is not to dwell upon the details of the anat- 

 omy of the subclass of Cyclostomata, 1 which includes the families of 

 Petromyzontidce and Myxinidce, and is fully given in the works of 

 Miiller, Owen, Huxley, Giinther, and other authors, I will simply 

 call attention to some points in the anatomy of the specimens of 

 Rlyxine before us. The body is eel-shaped, and is covered by a 

 thin skin, which is easily detached. Along the under side, for very 

 nearly the whole length of the animal, are two rows of mucous 

 glands, each gland having an external opening, and from these, dur- 



1 Also known under the names Marsipobrancliii and Myzontes. The lancelet is 

 excluded, for from our present ideas of the limits of groups I am inclined to re- 

 gard this single species as representing the lowest subclass of vertebrates, the 

 Leptocardii. 



