SURFACE-SWIMMING FAUNA (INVERTEBRATES). 87 



long antennae, projecting from the head end of 

 the body. They occur in fresh water as well as in 

 the sea, and so abundant are they that if a glass 

 tumbler be filled with the water from a pond, a 

 lake, or the sea, and examined with a magnify- 

 ing glass, a number of specimens are almost sure 

 to be seen. They occur in abundance at the 

 surface of the sea in nearly all climes, and very 

 often are the sole representatives of the Plank- 

 ton that are found in the hauls of the tow- 

 net. 



Attention has already been called above to 

 the fact that in the Tropics the surface-floating 

 animals gradually sink down into the depths 

 as the heat of the day approaches, but even on 

 fine calm days a few Copepods will be found at 

 the surface. Although they sometimes occur in 

 Temperate seas in such vast numbers that the 

 water is quite discoloured with them, more 

 variety of form, or, in other words, more distinct 

 genera and species are found in the warm and 

 Tropical parts of the world. 



The study of this group reveals to the micro- 

 scopist some of the most marvellously beautiful 

 displays of colour and form that can be found in 

 the animal kingdom. Sometimes the body and 

 legs are beset with an immense number of 

 extremely fine and delicate spines, which are 

 in some cases provided with rows of still 

 finer spinelets, giving them the appearance of 

 a most minute feather. Sometimes the body 

 contains large granules of a bright-red colour, 

 and at others smaller granules of a bright 

 blue are seen scattered among the organs. The 



