iv. 5 



SWIMMING OF LAMPREYS 



85 



The lamprey swims with an eel-like motion, using its myotomes in 

 the serial manner that has been mentioned in amphioxus and will be 

 discussed later (p. 133). The waves that pass down the body are of 

 short period relative to the length, so that the swimming is mechani- 

 cally inefficient; lampreys show great activity, but their progress is 

 not rapid. The animal often comes to rest, attaching itself with the 

 sucker to stones (hence the name, 'suck-stone') or to its prey. In this 

 position water cannot of course pass in through the mouth, but both 



s. cut. 



Fig. 48. Section of skin of lamprey. 



c. club cells; der. dermis; ep. epidermis; gr. granular gland-cells; m. myotomal muscle; 

 pig. pigment cells; s.cut. subcutaneous connective tissue. (After Krause.) 



enters and leaves by the gill openings. When swimming the backward 

 jet of water may assist in locomotion. 



The trunk musculature consists of a series of myotomes separated 

 by myocommas. Each myotome has a W-shape, instead of the simple 

 V of amphioxus. The muscle-fibres run longitudinally and they are 

 striped, but of a somewhat peculiar fenestrated type. 



5. Skeleton of lampreys 



The skeleton of lampreys consists of the notochord and various 

 collections of cartilage. This latter is partly of the typical vertebrate 

 type, that is to say, consists of large cells in groups, separated by a 

 matrix of the protein chondrin, which they secrete. In other regions 

 a tissue containing more cells and less matrix is found, the so-called 

 fibro-cartilage, and this more nearly resembles fibrous connective 

 tissue and serves to emphasize that no sharp line can be drawn 

 between these tissues. There is also, in the larva, a tissue known as 



