i] THE CATEGORIES OF LIFE 27 



Generally speaking the bulk of the plankton is 

 made up of larval invertebrates, Diatoms, Peridineans, 

 and some groups of micro-crustacea, the Copepods 

 mainly, which live permanently in the plankton. 

 There is this general relation between the abundance 

 of the Diatoms, or Peridinians, and that of the 

 Microcrustacea, such as the Copepods, that when one 

 is abundant, the other group is scarce. There are, 

 of course many other planktonic animals and plants. 

 The larger rooted algae are represented by their 

 zoospores. Many molluscs are permanently plank- 

 tonic thus the Pteropods are abundant enough to 

 form the food of the whale, and to constitute a large 

 part of the sea-bottom deposits in some regions of 

 ocean. Many medusae and other jelly fishes are also 

 planktonic. 



The Naturalist's Dredge. 



