SURFACE-SWIMMING FAUNA (INVERTEBRATES). 95 



gives them that soft jelly-like consistency which 

 is so characteristic of the surface - swimming 

 forms. 



The popular term ' Jelly-fish' is one that is 

 frequently applied to many forms of surface- 

 swimming animals that are really very different 

 in structure and general composition from the 

 true Medusae. The Salps, for example, to which 

 reference will be made presently, although soft 

 and transparent in texture like the Medusae, 

 belong to a very widely separated group of 

 animals, and to the anatomist it would be as 

 absurd to classify them together, as to put the 

 Butterflies and the Fish in the same group. 



These remarks are necessary because in the 

 treatment adopted in this little book the animals 

 that live together are considered in the same 

 chapter, and it is important that the reader 

 should bear in mind that they are not as a 

 consequence anatomically related to one another. 



It is indeed remarkable that animals which 

 are so different from one another, in their 

 anatomy, development and life history, as, for 

 example, the Salps and the Medusae, and which 

 have had such a widely different ancestry, 

 should, as a matter of fact, resemble one 

 another so closely in form and texture as to be 

 given collectively the same name by the unscien- 

 tific observer. 



Among the heterogeneous crowd of animals 

 that are popularly called Jelly-fish there is one 

 particular group which presents us with some 

 very interesting members. These are the 

 Siphonophores. In many parts of the temperate 



