308 THE SEA SHORE 



found in our seas, and will receive a short notice here. The fishes 

 will, of course, demand a fair share of our attention. Amphibians 

 and reptiles have no British marine representatives, and are there- 

 fore quite excluded from this work. As to the birds, although there 

 are so many that live entirely on the sea and in its immediate 

 neighbourhood, these have been so ably dealt with by Mr. Hudson 

 in one of the books of this series that it would be superfluous to 

 mention them. The mammals include a considerable number of 

 marine species, but as only one of these the Porpoise is really 

 commonly observed round our coasts, it alone will be selected for 

 description. 



Lampreys and their few allies were formerly classified with 

 fishes, but are now made to form a small class by themselves ; and 

 there is abundant reason for the separation. It will be remembered 

 that vertebrates, in the early stages of their development, are charac- 

 terised by a cartilaginous rod running through the dorsal region of 

 the bod}', below the central cord of the nervous system, and that they 

 possess a series of slits opening into the sides of the pharynx. Now, 

 while these characteristics are usually only transitory in the verte- 

 brates, the Lampreys and their relatives are the only animals in 

 which they persist throughout life, and it is for this reason that they 

 are exalted to the dignity of a class under the title Cyclostomata. 



This name signifies ' round-mouthed,' while the Lampreys them- 

 selves form the still smaller division Marsipobranchii, which means 

 ' pouch-gilled,' these two being among the most evident characters 

 of the creatures concerned. They have no true jaws, the circular 

 mouth being supported by a ring of cartilage, and provided with a 

 rasp-like tongue that enables them to divide their food. They have 

 no true bone in their bodies, the simple skeleton, without limbs 

 and ribs, being entirely cartilaginous, and the rudimentary skull is 

 not movable on the dorsal cartilage. Their bodies are elongated 

 and eel-like, with a single medial fin, supported by fine cartilaginous 

 rays, and with seven little slits on each side of the neck, communi- 

 cating with as many gills in the form of little pouches. The mouth 

 is suctorial, presenting, when open, a circular adhesive disc, by 

 which the animals can attach themselves to any solid object, but 

 assumes the form of a mere slit when closed. The young differ 

 from the adult in a few points of structure. Thus they have no 

 eyes, and the long fin, divided in the adult, is continuous. With 

 the above characteristics in mind, there will be no danger of con- 

 fusing the lampreys with the eels and other similar fishes. 



