Tiinicata. 87 



after attaining- a certain size. Like Pyrosoma the Salpse are phosphor- 

 escent animals. 



In connection with the Tunicata we may mention the Lancelets, 

 which are looked upon as the lowest vertebrate animals. The Neapolitan 

 Lancelet , Amphioxus laneeolatus (Fig. 6G) , is scarcely 2 inches long , 

 colourless and translucent ; its only skeleton is a notochord ; it has no 

 head. Instead of a heart it has pulsating vessels containing colourless 

 blood , and like the Tunicates it has a throat perforated with many 

 gill-slits. But its development is even of greater interest to zoologists 

 than its anatomy ; for it resembles greatly that of the Ascidians (cp. 

 p. 85) and points to a near relationship of these two groups. It is sup- 

 posed that there must once have existed a group of animals possessing a 

 notochord and gill-slits, whose descendants are now represented by three 

 clans , (1) the Fishes and Terrestrial Vertebrates , (2) the Lancelets , (3) 

 the Tunicates. 



Amphioxus lives in the sand of flat coasts and resembles a worm 

 more than a fish. It is found in thousands along the beach of Posilipo 

 and similar tracts of the Bay of Naples. It was first discovered on 

 British coasts by Mr. Couch in 1881 ; within the last few years several 

 kinds of Lancelets have been found in other seas. 



In the Aquarium it can only be kept , if a plentiful supplj^ of sand 

 be in the tank (the little open one in front of tank Nr. 10). In this it 

 burrows immediatelv and onlv comes out at night or if disturbed. 



'&■ 



FISHES (PISCES). 



Fishes have such well-known external characters, that they will be 

 rarely mistaken for members of the other large groups of the animal 

 kingdom. We will only remind the reader that the « cuttlefish » are not 

 really « fishes » in the zoological sense but mollusks, and that there are 

 a few true fishes differing considerably from the usual form, such as the 

 snake-like eels, the flattened rays and soles, and the graceful sea-horses. 



As the fishes, like the other animals, are arranged in the Aquarium 

 so as to suit their various modes of life , we shall also arrange our 

 remarks to illustrate the same. Scientifically the fishes are divided into 

 cartilaginous and bony fishes respectively, but in both groups according 

 to their hal>its Ave can distinguish Drift-fishes , that is such kinds as are 

 always or almost always swimming , and Bottom-fishes , which pass the 

 greater part of their life lying on or even buried in the sand , or on 

 the rocks. This distinction cannot , of course , be carried through quite 

 consistently, as we find all sorts of intermediate kinds. 



We will begin with the Cartilaginous Fishes, to which the Sharks, 

 Dog-fish, and Rays belong. Those in the Aquarium are chiefly Bottom- 

 fishes , which display only very little of their life. Let us turn our 

 attention first of all to the SJmrks. 



The word « Sliark » will cause the reader to think at once of those 

 gigantic robbers of the ocean, which have become the terror of the sai- 



